Many of you have tried embedding YouTube video in webpage using EMBED tag. It’s very easy. Just copy the code and paste it in webpage, it will start streaming video. You may think, what’s new here? Yes, you are right there is nothing tricky here. Wait for a while.
Check the second scenario. Let say you want to steam any random video (.flv) other than YouTube video. What options do you have? Either you can use built in flash video player with little customization to match look and feel with your website theme or you can use free open source flash video player (e.g. flowplayer) to stream your video. So, what’s exciting here? Nothing.
Now check the third scenario. Let say you want to steam video provided by YouTube, but want to change video skin to match look and feel with your website? What you will do? Is there any option available to change skin of YouTube player other than default skin?
Yes; it’s possible. You can choose “YouTube Custom Player” if you just want to change background color, name of the player and content of default YouTube player. Or you can user “YouTube Chromeless Player”. You can use either JavaScript APIs or Flash APIs to make your custom player.
See the demo here; cromeless player using JavaScript APIs.
I found some limitation in integrating this APIs
(1) YouTube has provided numerous functions to integrate. But it’s hard to control various events like play, pause, mute, un-mute etc. in design.
(2) The given example support embedding of only one video player at a time. What to do if you have more than one video on a webpage?
I have made a JavaScript class using JavaScript APIs which allows user to overcome both the listed issues.
You can download the class and example code here!
Also, check the demo here of what I have implemented.
If you find any difficulties using this class, please contact me.
Hope you will find this post helpful.
Saturday, January 31, 2009
Thursday, January 29, 2009
Use a CDN to improve your website's performance
"80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Rather than starting with the difficult task of redesigning your application architecture, it's better to first disperse your static content. This will achieves a bigger reduction in response times." - Steve Saunders
Performance, Scalability and Cost efficiency to end users are main key factors for any web application. CDN (content delivery network) is the solution to achieve it. A CDN can offer 100% availability, even with large power, network or hardware outages. Traditional CDNs focus on web acceleration. New CDNs have integrated media delivery services so they are optimized for live video streaming, high definition video and large asset delivery.
Why we need to use CDN?
The main point of the CDN is caching. So, it definitely helps in improving performance and scalability of a website.
When not to use a CDN?
- Whenever you’re working offline.
- When you can deliver faster than the CDN, and care about that. This might be the case when all users are close to the server.
Privacy and security concerns.
Using the CDN, you are trusting the CDN to faithfully serve contents and relying on no third-parties injecting funniness in between the CDN and your user’s browser. It's good to use a reliable CDN like "Google’s The AJAX Libraries API"
The AJAX Libraries API is a content distribution network and loading architecture for the most popular, open source JavaScript libraries. By using the Google AJAX API Loader's google.load() method, your application has high speed, globally available access to a growing list of the most popular, open source JavaScript libraries including: jQuery, jQuery UI, Prototype, script.aculo.us, MooTools, Dojo, SWFObject and YUI
Try it in your web application to see performance improvement in your application.
Performance, Scalability and Cost efficiency to end users are main key factors for any web application. CDN (content delivery network) is the solution to achieve it. A CDN can offer 100% availability, even with large power, network or hardware outages. Traditional CDNs focus on web acceleration. New CDNs have integrated media delivery services so they are optimized for live video streaming, high definition video and large asset delivery.
Why we need to use CDN?
The main point of the CDN is caching. So, it definitely helps in improving performance and scalability of a website.
When not to use a CDN?
- Whenever you’re working offline.
- When you can deliver faster than the CDN, and care about that. This might be the case when all users are close to the server.
Privacy and security concerns.
Using the CDN, you are trusting the CDN to faithfully serve contents and relying on no third-parties injecting funniness in between the CDN and your user’s browser. It's good to use a reliable CDN like "Google’s The AJAX Libraries API"
The AJAX Libraries API is a content distribution network and loading architecture for the most popular, open source JavaScript libraries. By using the Google AJAX API Loader's google.load() method, your application has high speed, globally available access to a growing list of the most popular, open source JavaScript libraries including: jQuery, jQuery UI, Prototype, script.aculo.us, MooTools, Dojo, SWFObject and YUI
Try it in your web application to see performance improvement in your application.
Monday, January 26, 2009
Book Review: High Performance Web Sites - Steve Souders
High Performance Web Sites by Steve Souders is one of the most important books front end engineers should read to be able to develop a proper web sites. In 14 chapter, you will know 14 of the best tips to enhance the performance of your website. the author gives example by numbers and statistics about the top 10 websites on the internet. In each tip Steve tells the effect of applying this tip on the top 10 websites.
This book is short and definitely very good in term of contents. The subtitle is, "Essential Knowledge for Frontend Engineers." The book is a quick read compared to most technical books, and not just due to its relatively small size (168 pages), but also the writing style.
According to Joe (Developer of Firebug debugger and Mozilla's DOM Inspector) -
"If everyone would implement just 20% of Steve's guidelines, the Web would be a dramatically better place. Between this book and Steve's YSlow extension, there's really no excuse for having a sluggish web site anymore."
Each performance rule in the book is supported by specific examples, and code snippets are available on the book's companion web site. The rules include how to:
* Make Fewer HTTP Requests
* Use a Content Delivery Network
* Add an Expires Header
* Gzip Components
* Put Stylesheets at the Top
* Put Scripts at the Bottom
* Avoid CSS Expressions
* Make JavaScript and CSS External
* Reduce DNS Lookups
* Minify JavaScript
* Avoid Redirects
* Remove Duplicates Scripts
* Configure ETags
* Make Ajax Cacheable
Here I have shared a presentation by Steve Souders and Tenni Theurer on
"High Performance Web Sites"
This book is short and definitely very good in term of contents. The subtitle is, "Essential Knowledge for Frontend Engineers." The book is a quick read compared to most technical books, and not just due to its relatively small size (168 pages), but also the writing style.
According to Joe (Developer of Firebug debugger and Mozilla's DOM Inspector) -
"If everyone would implement just 20% of Steve's guidelines, the Web would be a dramatically better place. Between this book and Steve's YSlow extension, there's really no excuse for having a sluggish web site anymore."
Each performance rule in the book is supported by specific examples, and code snippets are available on the book's companion web site. The rules include how to:
* Make Fewer HTTP Requests
* Use a Content Delivery Network
* Add an Expires Header
* Gzip Components
* Put Stylesheets at the Top
* Put Scripts at the Bottom
* Avoid CSS Expressions
* Make JavaScript and CSS External
* Reduce DNS Lookups
* Minify JavaScript
* Avoid Redirects
* Remove Duplicates Scripts
* Configure ETags
* Make Ajax Cacheable
Here I have shared a presentation by Steve Souders and Tenni Theurer on
"High Performance Web Sites"
How to reduce the size of JavaScript & CSS file?
Compress JavaScript / CSS file with the help of gzip:-
With the help of php ob_start() function we can create gzip file for JavaScript.
<?php
if (substr_count($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip'))
ob_start("ob_gzhandler");
else
ob_start();
?>
We can use above code at the beginning of the JavaScript and <? Ob_flush();?> code at the end. So output of Php file is JavaScript code in gzip encrypted form.
In this method, we have to save JavaScript files as a .php file.
By compressing the plan text JavaScript file with the help of gzip; its size gets reduced by more than 60%. Smaller the file size, better the download time.
Reduce the size of JavaScript and CSS file by removing the white spaces, carriage return and comments:-
We can also remove the white spaces, carriage return and comments from JavaScript files to reduce its size. Every single letter or space in your HTML code takes up one byte. It doesn't sound like much but it all adds up. By working through page source and eliminating unnecessary white space and comments, we can shave off up to, or even over 10% of its file size.
With the help of php ob_start() function we can create gzip file for JavaScript.
<?php
if (substr_count($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip'))
ob_start("ob_gzhandler");
else
ob_start();
?>
We can use above code at the beginning of the JavaScript and <? Ob_flush();?> code at the end. So output of Php file is JavaScript code in gzip encrypted form.
In this method, we have to save JavaScript files as a .php file.
By compressing the plan text JavaScript file with the help of gzip; its size gets reduced by more than 60%. Smaller the file size, better the download time.
Reduce the size of JavaScript and CSS file by removing the white spaces, carriage return and comments:-
We can also remove the white spaces, carriage return and comments from JavaScript files to reduce its size. Every single letter or space in your HTML code takes up one byte. It doesn't sound like much but it all adds up. By working through page source and eliminating unnecessary white space and comments, we can shave off up to, or even over 10% of its file size.
Saturday, January 24, 2009
Is losing a job is terrible experience? Turn it into an opportunity!
In last couple of months, we have heard lots of job cuts/layoffs in various field. According to Techcrunch, 80,076 job eliminations have been announced or completed since the beginning of the year in the tech industry. The total number of tech layoffs since late August is now 195,856. The number is big and is growing fast.
No one likes to be told to leave the job. But the reality is that it happens every day in the corporate world more so in the bad economy. Those who are asked to pack up aren’t always non-performers. There are several reasons behind it!
(a) company is not performing well.
(b) employees are overqualified
(c) their position has become redundant because the company does not want to pursue the project/business that they were involved in etc.
When I was working with my previous employer, I got a chance to have a quick look of this situation. See some example below.
(a) I was a part of technical team while interviewing a Sr. Developer. There were two positions open and the person was hired with high expectation. Considering seniority of the hired person, second position was closed. The same person got fired after 4 months due to tech layoffs started at company. The clear reason I see here is; "The person failed to perform his duty well or the expectations were too high for him"
(b) two or three employees got best performance award and those too got laid off. I still don’t understand why they laid off.
(c) So many senior persons from middle management resigned. What could be the reason? "Fear of being laid off?"
(d) Some senior persons from top management got fired. Clear reason - "Cost cutting / changes in management to apply new strategies"
Those who got fired were either fresher, experienced persons - who recently joined company or top management executives.
Apart from this if good employees get laid off; means company is really not performing well and cash flow is not enough to survive.
The firing news can hit you hard. Shock and anger are usual feelings, however in some cases it can lead to depression too. One of my colleague had postponed his marriage due to layoff news. How do you cope up with such negative feelings? How do you tell yourself and the world that you are a capable professional? That you have what it takes to be successful.
Some suggestions to handle this situation.
(a) Don't Blame Yourself. Have confidence in yourself. See the job loss as an opportunity to make a new beginning. Job is part of life; but life is not part of job.
(b) Always have a network of good industry friends/contacts. It is this network that you can tap into when you suddenly find yourself on road with no job in hands.
(c) Manage Finances Well.
(d) Even if you are safe; stay in touch with your work technology. This will help you to survive in bad time.
(e) Talk to your HR to help you in finding new job. At our company, management gave good compensation to employees who got laid off and also, they made arrangement with job consultant to help who got fired. You may feel so angry and upset that you don't want to take any help whatsoever from the same employer who gave you the pink slip at the first place, but relationship matters.
(f) Lots of people are there who believe that "You are fired means you are not performing well", but I see - scenario is changed now. People understand that this is not the only reason why employee gets fired. After layoff at our company I interviewed two employees who got laid off recently from another well-known IT company. One of them got selected after interview due to his capabilities. So, be sincere and honest with the prospective employers about your last job. It's always better that they hear the truth from you than from someone else.
Have confidence in your abilities and move on.
No one likes to be told to leave the job. But the reality is that it happens every day in the corporate world more so in the bad economy. Those who are asked to pack up aren’t always non-performers. There are several reasons behind it!
(a) company is not performing well.
(b) employees are overqualified
(c) their position has become redundant because the company does not want to pursue the project/business that they were involved in etc.
When I was working with my previous employer, I got a chance to have a quick look of this situation. See some example below.
(a) I was a part of technical team while interviewing a Sr. Developer. There were two positions open and the person was hired with high expectation. Considering seniority of the hired person, second position was closed. The same person got fired after 4 months due to tech layoffs started at company. The clear reason I see here is; "The person failed to perform his duty well or the expectations were too high for him"
(b) two or three employees got best performance award and those too got laid off. I still don’t understand why they laid off.
(c) So many senior persons from middle management resigned. What could be the reason? "Fear of being laid off?"
(d) Some senior persons from top management got fired. Clear reason - "Cost cutting / changes in management to apply new strategies"
Those who got fired were either fresher, experienced persons - who recently joined company or top management executives.
Apart from this if good employees get laid off; means company is really not performing well and cash flow is not enough to survive.
The firing news can hit you hard. Shock and anger are usual feelings, however in some cases it can lead to depression too. One of my colleague had postponed his marriage due to layoff news. How do you cope up with such negative feelings? How do you tell yourself and the world that you are a capable professional? That you have what it takes to be successful.
Some suggestions to handle this situation.
(a) Don't Blame Yourself. Have confidence in yourself. See the job loss as an opportunity to make a new beginning. Job is part of life; but life is not part of job.
(b) Always have a network of good industry friends/contacts. It is this network that you can tap into when you suddenly find yourself on road with no job in hands.
(c) Manage Finances Well.
(d) Even if you are safe; stay in touch with your work technology. This will help you to survive in bad time.
(e) Talk to your HR to help you in finding new job. At our company, management gave good compensation to employees who got laid off and also, they made arrangement with job consultant to help who got fired. You may feel so angry and upset that you don't want to take any help whatsoever from the same employer who gave you the pink slip at the first place, but relationship matters.
(f) Lots of people are there who believe that "You are fired means you are not performing well", but I see - scenario is changed now. People understand that this is not the only reason why employee gets fired. After layoff at our company I interviewed two employees who got laid off recently from another well-known IT company. One of them got selected after interview due to his capabilities. So, be sincere and honest with the prospective employers about your last job. It's always better that they hear the truth from you than from someone else.
Have confidence in your abilities and move on.
Wednesday, January 21, 2009
Add a user to a group under Linux operating system
One can use useradd or usermod commands to add a user to a group. useradd command creates a new user or update default new user information. usermod command modifies a user account i.e. it is useful to add user to existing group. There are two types of group. First is primary user group and other is secondary group. All user account related information is stored in /etc/passwd, /etc/shadow and /etc/group files to store user information.
useradd example - Add a new user to secondary group
Use useradd command to add new users to existing group (or create a new group and then add user). If group does not exist, create it.
Syntax:
useradd -G {group-name} username
Create a new user called lamptech and add it to group called developers. First login as a root user (make sure group developers exists), enter:
# grep developers /etc/group
Output:
developers:x:1124:
If you do not see any output then you need to add group developers using groupadd command:
# groupadd developers
Next, add a user called lamptech to group developers:
# useradd -G developers lamptech
Setup password for user lamptech:
# passwd lamptech
Ensure that user added properly to group developers:
# id lamptech
Output:
uid=1122(lamptech) gid=1125(lamptech) groups=1125(lamptech),1124(developers)
Please note that capital G (-G) option add user to a list of supplementary groups. Each group is separated from the next by a comma, with no intervening whitespace. For example, add user jerry to groups admins, ftp, www, and developers, enter:
# useradd -G admins,ftp,www,developers jerry
useradd example - Add a new user to primary group
To add a user tony to group developers use following command:
# useradd -g developers tony
# id tony
uid=1123(tony) gid=1124(developers) groups=1124(developers)
Please note that small -g option add user to initial login group (primary group). The group name must exist. A group number must refer to an already existing group.
usermod example - Add a existing user to existing group
Add existing user tony to ftp supplementary/secondary group with usermod command using -a option ~ i.e. add the user to the supplemental group(s). Use only with -G option :
# usermod -a -G ftp tonyChange existing user tony primary group to www:
# usermod -g www tony
useradd example - Add a new user to secondary group
Use useradd command to add new users to existing group (or create a new group and then add user). If group does not exist, create it.
Syntax:
useradd -G {group-name} username
Create a new user called lamptech and add it to group called developers. First login as a root user (make sure group developers exists), enter:
# grep developers /etc/group
Output:
developers:x:1124:
If you do not see any output then you need to add group developers using groupadd command:
# groupadd developers
Next, add a user called lamptech to group developers:
# useradd -G developers lamptech
Setup password for user lamptech:
# passwd lamptech
Ensure that user added properly to group developers:
# id lamptech
Output:
uid=1122(lamptech) gid=1125(lamptech) groups=1125(lamptech),1124(developers)
Please note that capital G (-G) option add user to a list of supplementary groups. Each group is separated from the next by a comma, with no intervening whitespace. For example, add user jerry to groups admins, ftp, www, and developers, enter:
# useradd -G admins,ftp,www,developers jerry
useradd example - Add a new user to primary group
To add a user tony to group developers use following command:
# useradd -g developers tony
# id tony
uid=1123(tony) gid=1124(developers) groups=1124(developers)
Please note that small -g option add user to initial login group (primary group). The group name must exist. A group number must refer to an already existing group.
usermod example - Add a existing user to existing group
Add existing user tony to ftp supplementary/secondary group with usermod command using -a option ~ i.e. add the user to the supplemental group(s). Use only with -G option :
# usermod -a -G ftp tonyChange existing user tony primary group to www:
# usermod -g www tony
How to get domain name from URL using javascript.
Use following javascript function to get domain name from URL.
function fnGetDomain(url) {
return url.match(/:\/\/(.[^/]+)/)[1];
}
For ex: <script language="javascript">fnGetDomain("http://mail.google.com/mail/?source=navclient-ff");</script> will return "mail.google.com"
function fnGetDomain(url) {
return url.match(/:\/\/(.[^/]+)/)[1];
}
For ex: <script language="javascript">fnGetDomain("http://mail.google.com/mail/?source=navclient-ff");</script> will return "mail.google.com"
Monday, January 19, 2009
A multi-user blog system in PHP - Bluetrait
Blog systems are now very popular and there are plenty of solutions to implement blogs.
"Bluetrait" allows the one or more users to login and post articles that are stored in a database. Currently it supports storing posts in MySQL and SQLite posts.
It supports post categories, comments, comment spam filtering, generating RSS feeds, trackback handling and plug-in extensions.
Download Here!
Ref: http://www.bluetrait.com
"Bluetrait" allows the one or more users to login and post articles that are stored in a database. Currently it supports storing posts in MySQL and SQLite posts.
It supports post categories, comments, comment spam filtering, generating RSS feeds, trackback handling and plug-in extensions.
Download Here!
Ref: http://www.bluetrait.com
Get the contacts of friends of different e-mail providers and social networks - Open Inviter
Retrieving the contacts of users is often used by social networks and similar sites to get viral by attracting the users' friends.
"Open Inviter" is the solution. It can be use to get the contacts of friends of different e-mail providers and social networks.
It can access the Web services servers of different networks to retrieve the contacts of friends of a given user.
Each network is accessed by the means of plug-in classes. Some plug-ins support sending invitation messages to friends to be added to the user contacts.
Currently it comes with plug-ins that support many networks such as:
* AOL * GMail * GMX.net * Windows Live (Hotmail) * Katamail * Lycos * Mail.com * Mail.ru * Rambler.ru * Rediff * Yahoo! * Yandex * Facebook * Hi5 * LinkedIn * MySpace * Orkut * Twitter
Download Here!
Ref: http://openinviter.com
"Open Inviter" is the solution. It can be use to get the contacts of friends of different e-mail providers and social networks.
It can access the Web services servers of different networks to retrieve the contacts of friends of a given user.
Each network is accessed by the means of plug-in classes. Some plug-ins support sending invitation messages to friends to be added to the user contacts.
Currently it comes with plug-ins that support many networks such as:
* AOL * GMail * GMX.net * Windows Live (Hotmail) * Katamail * Lycos * Mail.com * Mail.ru * Rambler.ru * Rediff * Yahoo! * Yandex * Facebook * Hi5 * LinkedIn * MySpace * Orkut * Twitter
Download Here!
Ref: http://openinviter.com
How to apply TinyMCE editor only to specific Textarea?
By default, TinyMCE applies to every textarea of a HTML page. There is a way to make it only load on like <textarea id="mceEditor">.
just add the attribute 'editor_selector' in tinyMCE.init . The value for this attribute is a css class name which should be used in the textarea where you want to apply editor.
For ex:
and in the textarea tag
just add the attribute 'editor_selector' in tinyMCE.init . The value for this attribute is a css class name which should be used in the textarea where you want to apply editor.
For ex:
tinyMCE.init({
mode : "textareas",
theme : "simple",
editor_selector :"mceEditor"
});
and in the textarea tag
<textarea name="description" style="width:100%;" class="mceEditor">
Sunday, January 11, 2009
Edit whatever you want on any page - Images, Texts
Open any web page, clear the address bar, and paste the code:
and hit enter. Feel free to edit whatever you want on the page. With Firefox, you can even edit and save the modified pages to your computer.
javascript:document.body.contentEditable='true'; document.designMode='on'; void 0;
and hit enter. Feel free to edit whatever you want on the page. With Firefox, you can even edit and save the modified pages to your computer.
Monday, January 5, 2009
Best Practices for Speeding Up Your Web Site - Yahoo! DN
Minimize HTTP Requests
tag: content
80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.
One way to reduce the number of components in the page is to simplify the page's design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.
Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all CSS into a single stylesheet. Combining files is more challenging when the scripts and stylesheets vary from page to page, but making this part of your release process improves response times.
CSS Sprites are the preferred method for reducing the number of image requests. Combine your background images into a single image and use the CSS background-image and background-position properties to display the desired image segment.
Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone. Using image maps for navigation is not accessible too, so it's not recommended.
Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages. Inline images are not yet supported across all major browsers.
Reducing the number of HTTP requests in your page is the place to start. This is the most important guideline for improving performance for first time visitors. As described in Tenni Theurer's blog post Browser Cache Usage - Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.
Use a Content Delivery Network
tag: server
The user's proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user's perspective. But where should you start?
As a first step to implementing geographically dispersed content, don't attempt to redesign your web application to work in a distributed architecture. Depending on the application, changing the architecture could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this application architecture step.
Remember that 80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. This is the Performance Golden Rule. Rather than starting with the difficult task of redesigning your application architecture, it's better to first disperse your static content. This not only achieves a bigger reduction in response times, but it's easier thanks to content delivery networks.
A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users. The server selected for delivering content to a specific user is typically based on a measure of network proximity. For example, the server with the fewest network hops or the server with the quickest response time is chosen.
Some large Internet companies own their own CDN, but it's cost-effective to use a CDN service provider, such as Akamai Technologies, Mirror Image Internet, or Limelight Networks. For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times. At Yahoo!, properties that moved static content off their application web servers to a CDN improved end-user response times by 20% or more. Switching to a CDN is a relatively easy code change that will dramatically improve the speed of your web site.
Add an Expires or a Cache-Control Header
tag: server
There are two things in this rule:
* For static components: implement "Never expire" policy by setting far future Expires header
* For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests
Web page designs are getting richer and richer, which means more scripts, stylesheets, images, and Flash in the page. A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable. This avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often used with images, but they should be used on all components including scripts, stylesheets, and Flash components.
Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won't be stale until April 15, 2010.
Expires: Thu, 15 Apr 2010 20:00:00 GMT
If your server is Apache, use the ExpiresDefault directive to set an expiration date relative to the current date. This example of the ExpiresDefault directive sets the Expires date 10 years out from the time of the request.
ExpiresDefault "access plus 10 years"
Keep in mind, if you use a far future Expires header you have to change the component's filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component's filename, for example, yahoo_2.0.6.js.
Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A "primed cache" already contains all of the components in the page.) We measured this at Yahoo! and found the number of page views with a primed cache is 75-85%. By using a far future Expires header, you increase the number of components that are cached by the browser and re-used on subsequent page views without sending a single byte over the user's Internet connection.
Gzip Components
tag: server
The time it takes to transfer an HTTP request and response across the network can be significantly reduced by decisions made by front-end engineers. It's true that the end-user's bandwidth speed, Internet service provider, proximity to peering exchange points, etc. are beyond the control of the development team. But there are other variables that affect response times. Compression reduces response times by reducing the size of the HTTP response.
Starting with HTTP/1.1, web clients indicate support for compression with the Accept-Encoding header in the HTTP request.
Accept-Encoding: gzip, deflate
If the web server sees this header in the request, it may compress the response using one of the methods listed by the client. The web server notifies the web client of this via the Content-Encoding header in the response.
Content-Encoding: gzip
Gzip is the most popular and effective compression method at this time. It was developed by the GNU project and standardized by RFC 1952. The only other compression format you're likely to see is deflate, but it's less effective and less popular.
Gzipping generally reduces the response size by about 70%. Approximately 90% of today's Internet traffic travels through browsers that claim to support gzip. If you use Apache, the module configuring gzip depends on your version: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate.
There are known issues with browsers and proxies that may cause a mismatch in what the browser expects and what it receives with regard to compressed content. Fortunately, these edge cases are dwindling as the use of older browsers drops off. The Apache modules help out by adding appropriate Vary response headers automatically.
Servers choose what to gzip based on file type, but are typically too limited in what they decide to compress. Most web sites gzip their HTML documents. It's also worthwhile to gzip your scripts and stylesheets, but many web sites miss this opportunity. In fact, it's worthwhile to compress any text response including XML and JSON. Image and PDF files should not be gzipped because they are already compressed. Trying to gzip them not only wastes CPU but can potentially increase file sizes.
Gzipping as many file types as possible is an easy way to reduce page weight and accelerate the user experience.
Put Stylesheets at the Top
tag: css
While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively.
Front-end engineers that care about performance want a page to load progressively; that is, we want the browser to display whatever content it has as soon as possible. This is especially important for pages with a lot of content and for users on slower Internet connections. The importance of giving users visual feedback, such as progress indicators, has been well researched and documented. In our case the HTML page is the progress indicator! When the browser loads the page progressively the header, the navigation bar, the logo at the top, etc. all serve as visual feedback for the user who is waiting for the page. This improves the overall user experience.
The problem with putting stylesheets near the bottom of the document is that it prohibits progressive rendering in many browsers, including Internet Explorer. These browsers block rendering to avoid having to redraw elements of the page if their styles change. The user is stuck viewing a blank white page.
The HTML specification clearly states that stylesheets are to be included in the HEAD of the page: "Unlike A, [LINK] may only appear in the HEAD section of a document, although it may appear any number of times." Neither of the alternatives, the blank white screen or flash of unstyled content, are worth the risk. The optimal solution is to follow the HTML specification and load your stylesheets in the document HEAD.
Put Scripts at the Bottom
tag: javascript
The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won't start any other downloads, even on different hostnames.
In some situations it's not easy to move scripts to the bottom. If, for example, the script uses document.write to insert part of the page's content, it can't be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.
An alternative suggestion that often comes up is to use deferred scripts. The DEFER attribute indicates that the script does not contain document.write, and is a clue to browsers that they can continue rendering. Unfortunately, Firefox doesn't support the DEFER attribute. In Internet Explorer, the script may be deferred, but not as much as desired. If a script can be deferred, it can also be moved to the bottom of the page. That will make your web pages load faster.
Avoid CSS Expressions
tag: css
CSS expressions are a powerful (and dangerous) way to set CSS properties dynamically. They're supported in Internet Explorer, starting with version 5. As an example, the background color could be set to alternate every hour using CSS expressions.
background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );
As shown here, the expression method accepts a JavaScript expression. The CSS property is set to the result of evaluating the JavaScript expression. The expression method is ignored by other browsers, so it is useful for setting properties in Internet Explorer needed to create a consistent experience across browsers.
The problem with expressions is that they are evaluated more frequently than most people expect. Not only are they evaluated when the page is rendered and resized, but also when the page is scrolled and even when the user moves the mouse over the page. Adding a counter to the CSS expression allows us to keep track of when and how often a CSS expression is evaluated. Moving the mouse around the page can easily generate more than 10,000 evaluations.
One way to reduce the number of times your CSS expression is evaluated is to use one-time expressions, where the first time the expression is evaluated it sets the style property to an explicit value, which replaces the CSS expression. If the style property must be set dynamically throughout the life of the page, using event handlers instead of CSS expressions is an alternative approach. If you must use CSS expressions, remember that they may be evaluated thousands of times and could affect the performance of your page.
Make JavaScript and CSS External
tag: javascript, css
Many of these performance rules deal with how external components are managed. However, before these considerations arise you should ask a more basic question: Should JavaScript and CSS be contained in external files, or inlined in the page itself?
Using external files in the real world generally produces faster pages because the JavaScript and CSS files are cached by the browser. JavaScript and CSS that are inlined in HTML documents get downloaded every time the HTML document is requested. This reduces the number of HTTP requests that are needed, but increases the size of the HTML document. On the other hand, if the JavaScript and CSS are in external files cached by the browser, the size of the HTML document is reduced without increasing the number of HTTP requests.
The key factor, then, is the frequency with which external JavaScript and CSS components are cached relative to the number of HTML documents requested. This factor, although difficult to quantify, can be gauged using various metrics. If users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.
Many web sites fall in the middle of these metrics. For these sites, the best solution generally is to deploy the JavaScript and CSS as external files. The only exception where inlining is preferable is with home pages, such as Yahoo!'s front page and My Yahoo!. Home pages that have few (perhaps only one) page view per session may find that inlining JavaScript and CSS results in faster end-user response times.
For front pages that are typically the first of many page views, there are techniques that leverage the reduction of HTTP requests that inlining provides, as well as the caching benefits achieved through using external files. One such technique is to inline JavaScript and CSS in the front page, but dynamically download the external files after the page has finished loading. Subsequent pages would reference the external files that should already be in the browser's cache.
Reduce DNS Lookups
tag: content
The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map people's names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server's IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can't download anything from this hostname until the DNS lookup is completed.
DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user's ISP or local area network, but there is also caching that occurs on the individual user's computer. The DNS information remains in the operating system's DNS cache (the "DNS Client service" on Microsoft Windows). Most browsers have their own caches, separate from the operating system's cache. As long as the browser keeps a DNS record in its own cache, it doesn't bother the operating system with a request for the record.
Internet Explorer caches DNS lookups for 30 minutes by default, as specified by the DnsCacheTimeout registry setting. Firefox caches DNS lookups for 1 minute, controlled by the network.dnsCacheExpiration configuration setting. (Fasterfox changes this to 1 hour.)
When the client's DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page. This includes the hostnames used in the page's URL, images, script files, stylesheets, Flash objects, etc. Reducing the number of unique hostnames reduces the number of DNS lookups.
Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times. My guideline is to split these components across at least two but no more than four hostnames. This results in a good compromise between reducing DNS lookups and allowing a high degree of parallel downloads.
Minify JavaScript and CSS
tag: javascript, css
Minification is the practice of removing unnecessary characters from code to reduce its size thereby improving load times. When code is minified all comments are removed, as well as unneeded white space characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Two popular tools for minifying JavaScript code are JSMin and YUI Compressor. The YUI compressor can also minify CSS.
Obfuscation is an alternative optimization that can be applied to source code. It's more complex than minification and thus more likely to generate bugs as a result of the obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a 21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size reduction, minifying JavaScript is less risky.
In addition to minifying external scripts and styles, inlined <script> and <style> blocks can and should also be minified. Even if you gzip your scripts and styles, minifying them will still reduce the size by 5% or more. As the use and size of JavaScript and CSS increases, so will the savings gained by minifying your code.
Avoid Redirects
tag: content
Redirects are accomplished using the 301 and 302 status codes. Here's an example of the HTTP headers in a 301 response:
HTTP/1.1 301 Moved Permanently
Location: http://example.com/newuri
Content-Type: text/html
The browser automatically takes the user to the URL specified in the Location field. All the information necessary for a redirect is in the headers. The body of the response is typically empty. Despite their names, neither a 301 nor a 302 response is cached in practice unless additional headers, such as Expires or Cache-Control, indicate it should be. The meta refresh tag and JavaScript are other ways to direct users to a different URL, but if you must do a redirect, the preferred technique is to use the standard 3xx HTTP status codes, primarily to ensure the back button works correctly.
The main thing to remember is that redirects slow down the user experience. Inserting a redirect between the user and the HTML document delays everything in the page since nothing in the page can be rendered and no components can start being downloaded until the HTML document has arrived.
One of the most wasteful redirects happens frequently and web developers are generally not aware of it. It occurs when a trailing slash (/) is missing from a URL that should otherwise have one. For example, going to http://astrology.yahoo.com/astrology results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/ (notice the added trailing slash). This is fixed in Apache by using Alias or mod_rewrite, or the DirectorySlash directive if you're using Apache handlers.
Connecting an old web site to a new one is another common use for redirects. Others include connecting different parts of a website and directing the user based on certain conditions (type of browser, type of user account, etc.). Using a redirect to connect two web sites is simple and requires little additional coding. Although using redirects in these situations reduces the complexity for developers, it degrades the user experience. Alternatives for this use of redirects include using Alias and mod_rewrite if the two code paths are hosted on the same server. If a domain name change is the cause of using redirects, an alternative is to create a CNAME (a DNS record that creates an alias pointing from one domain name to another) in combination with Alias or mod_rewrite.
Remove Duplicate Scripts
tag: javascript
It hurts performance to include the same JavaScript file twice in one page. This isn't as unusual as you might think. A review of the ten top U.S. web sites shows that two of them contain a duplicated script. Two main factors increase the odds of a script being duplicated in a single web page: team size and number of scripts. When it does happen, duplicate scripts hurt performance by creating unnecessary HTTP requests and wasted JavaScript execution.
Unnecessary HTTP requests happen in Internet Explorer, but not in Firefox. In Internet Explorer, if an external script is included twice and is not cacheable, it generates two HTTP requests during page loading. Even if the script is cacheable, extra HTTP requests occur when the user reloads the page.
In addition to generating wasteful HTTP requests, time is wasted evaluating the script multiple times. This redundant JavaScript execution happens in both Firefox and Internet Explorer, regardless of whether the script is cacheable.
One way to avoid accidentally including the same script twice is to implement a script management module in your templating system. The typical way to include a script is to use the SCRIPT tag in your HTML page.
An alternative in PHP would be to create a function called insertScript.
In addition to preventing the same script from being inserted multiple times, this function could handle other issues with scripts, such as dependency checking and adding version numbers to script filenames to support far future Expires headers.
Configure ETags
tag: server
Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server. (An "entity" is another word a "component": images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component's ETag using the ETag response header.
HTTP/1.1 200 OK
Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
ETag: "10c24bc-4ab-457e1c1f"
Content-Length: 12195
Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.
GET /i/yahoo.gif HTTP/1.1
Host: us.yimg.com
If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
If-None-Match: "10c24bc-4ab-457e1c1f"
HTTP/1.1 304 Not Modified
The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.
The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Although a given file may reside in the same directory across multiple servers, and have the same file size, permissions, timestamp, etc., its inode is different from one server to the next.
IIS 5.0 and 6.0 have a similar issue with ETags. The format for ETags on IIS is Filetimestamp:ChangeNumber. A ChangeNumber is a counter used to track configuration changes to IIS. It's unlikely that the ChangeNumber is the same across all IIS servers behind a web site.
The end result is ETags generated by Apache and IIS for the exact same component won't match from one server to another. If the ETags don't match, the user doesn't receive the small, fast 304 response that ETags were designed for; instead, they'll get a normal 200 response along with all the data for the component. If you host your web site on just one server, this isn't a problem. But if you have multiple servers hosting your web site, and you're using Apache or IIS with the default ETag configuration, your users are getting slower pages, your servers have a higher load, you're consuming greater bandwidth, and proxies aren't caching your content efficiently. Even if your components have a far future Expires header, a conditional GET request is still made whenever the user hits Reload or Refresh.
If you're not taking advantage of the flexible validation model that ETags provide, it's better to just remove the ETag altogether. The Last-Modified header validates based on the component's timestamp. And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests. This Microsoft Support article describes how to remove ETags. In Apache, this is done by simply adding the following line to your Apache configuration file:
FileETag none
Make Ajax Cacheable
tag: content
One of the cited benefits of Ajax is that it provides instantaneous feedback to the user because it requests information asynchronously from the backend web server. However, using Ajax is no guarantee that the user won't be twiddling his thumbs waiting for those asynchronous JavaScript and XML responses to return. In many applications, whether or not the user is kept waiting depends on how Ajax is used. For example, in a web-based email client the user will be kept waiting for the results of an Ajax request to find all the email messages that match their search criteria. It's important to remember that "asynchronous" does not imply "instantaneous".
To improve performance, it's important to optimize these Ajax responses. The most important way to improve the performance of Ajax is to make the responses cacheable, as discussed in Add an Expires or a Cache-Control Header. Some of the other rules also apply to Ajax:
* Gzip Components
* Reduce DNS Lookups
* Minify JavaScript
* Avoid Redirects
* Configure ETags
Let's look at an example. A Web 2.0 email client might use Ajax to download the user's address book for autocompletion. If the user hasn't modified her address book since the last time she used the email web app, the previous address book response could be read from cache if that Ajax response was made cacheable with a future Expires or Cache-Control header. The browser must be informed when to use a previously cached address book response versus requesting a new one. This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612. If the address book hasn't been modified since the last download, the timestamp will be the same and the address book will be read from the browser's cache eliminating an extra HTTP roundtrip. If the user has modified her address book, the timestamp ensures the new URL doesn't match the cached response, and the browser will request the updated address book entries.
Even though your Ajax responses are created dynamically, and might only be applicable to a single user, they can still be cached. Doing so will make your Web 2.0 apps faster.
Flush the Buffer Early
tag: server
When users request a page, it can take anywhere from 200 to 500ms for the backend server to stitch together the HTML page. During this time, the browser is idle as it waits for the data to arrive. In PHP you have the function flush(). It allows you to send your partially ready HTML response to the browser so that the browser can start fetching components while your backend is busy with the rest of the HTML page. The benefit is mainly seen on busy backends or light frontends.
A good place to consider flushing is right after the HEAD because the HTML for the head is usually easier to produce and it allows you to include any CSS and JavaScript files for the browser to start fetching in parallel while the backend is still processing.
Example:
... <!-- css, js -->
</head>
<?php flush(); ?>
<body>
... <!-- content -->
Yahoo! search pioneered research and real user testing to prove the benefits of using this technique.
Use GET for AJAX Requests
tag: server
The Yahoo! Mail team found that when using XMLHttpRequest, POST is implemented in the browsers as a two-step process: sending the headers first, then sending data. So it's best to use GET, which only takes one TCP packet to send (unless you have a lot of cookies). The maximum URL length in IE is 2K, so if you send more than 2K data you might not be able to use GET.
An interesting side affect is that POST without actually posting any data behaves like GET. Based on the HTTP specs, GET is meant for retrieving information, so it makes sense (semantically) to use GET when you're only requesting data, as opposed to sending data to be stored server-side.
Post-load Components
tag: content
You can take a closer look at your page and ask yourself: "What's absolutely required in order to render the page initially?". The rest of the content and components can wait.
JavaScript is an ideal candidate for splitting before and after the onload event. For example if you have JavaScript code and libraries that do drag and drop and animations, those can wait, because dragging elements on the page comes after the initial rendering. Other places to look for candidates for post-loading include hidden content (content that appears after a user action) and images below the fold.
Tools to help you out in your effort: YUI Image Loader allows you to delay images below the fold and the YUI Get utility is an easy way to include JS and CSS on the fly. For an example in the wild take a look at Yahoo! Home Page with Firebug's Net Panel turned on.
It's good when the performance goals are inline with other web development best practices. In this case, the idea of progressive enhancement tells us that JavaScript, when supported, can improve the user experience but you have to make sure the page works even without JavaScript. So after you've made sure the page works fine, you can enhance it with some post-loaded scripts that give you more bells and whistles such as drag and drop and animations.
Preload Components
tag: content
Preload may look like the opposite of post-load, but it actually has a different goal. By preloading components you can take advantage of the time the browser is idle and request components (like images, styles and scripts) you'll need in the future. This way when the user visits the next page, you could have most of the components already in the cache and your page will load much faster for the user.
There are actually several types of preloading:
* Unconditional preload - as soon as onload fires, you go ahead and fetch some extra components. Check google.com for an example of how a sprite image is requested onload. This sprite image is not needed on the google.com homepage, but it is needed on the consecutive search result page.
* Conditional preload - based on a user action you make an educated guess where the user is headed next and preload accordingly. On search.yahoo.com you can see how some extra components are requested after you start typing in the input box.
* Anticipated preload - preload in advance before launching a redesign. It often happens after a redesign that you hear: "The new site is cool, but it's slower than before". Part of the problem could be that the users were visiting your old site with a full cache, but the new one is always an empty cache experience. You can mitigate this side effect by preloading some components before you even launched the redesign. Your old site can use the time the browser is idle and request images and scripts that will be used by the new site
Reduce the Number of DOM Elements
tag: content
A complex page means more bytes to download and it also means slower DOM access in JavaScript. It makes a difference if you loop through 500 or 5000 DOM elements on the page when you want to add an event handler for example.
A high number of DOM elements can be a symptom that there's something that should be improved with the markup of the page without necessarily removing content. Are you using nested tables for layout purposes? Are you throwing in more <div>s only to fix layout issues? Maybe there's a better and more semantically correct way to do your markup.
A great help with layouts are the YUI CSS utilities: grids.css can help you with the overall layout, fonts.css and reset.css can help you strip away the browser's defaults formatting. This is a chance to start fresh and think about your markup, for example use <div>s only when it makes sense semantically, and not because it renders a new line.
The number of DOM elements is easy to test, just type in Firebug's console:
document.getElementsByTagName('*').length
And how many DOM elements are too many? Check other similar pages that have good markup. For example the Yahoo! Home Page is a pretty busy page and still under 700 elements (HTML tags).
Split Components Across Domains
tag: content
Splitting components allows you to maximize parallel downloads. Make sure you're using not more than 2-4 domains because of the DNS lookup penalty. For example, you can host your HTML and dynamic content on www.example.org and split static components between static1.example.org and static2.example.org
Minimize the Number of iframes
tag: content
Iframes allow an HTML document to be inserted in the parent document. It's important to understand how iframes work so they can be used effectively.
<iframe> pros:
* Helps with slow third-party content like badges and ads
* Security sandbox
* Download scripts in parallel
<iframe> cons:
* Costly even if blank
* Blocks page onload
* Non-semantic
No 404s
tag: content
HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit.
Some sites have helpful 404s "Did you mean X?", which is great for the user experience but also wastes server resources (like database, etc). Particularly bad is when the link to an external JavaScript is wrong and the result is a 404. First, this download will block parallel downloads. Next the browser may try to parse the 404 response body as if it were JavaScript code, trying to find something usable in it.
Reduce Cookie Size
tag: cookie
HTTP cookies are used for a variety of reasons such as authentication and personalization. Information about cookies is exchanged in the HTTP headers between web servers and browsers. It's important to keep the size of cookies as low as possible to minimize the impact on the user's response time.
For more information check "When the Cookie Crumbles" by Tenni Theurer and Patty Chi. The take-home of this research:
* Eliminate unnecessary cookies
* Keep cookie sizes as low as possible to minimize the impact on the user response time
* Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected
* Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time
Use Cookie-free Domains for Components
tag: cookie
When the browser makes a request for a static image and sends cookies together with the request, the server doesn't have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.
If your domain is www.example.org, you can host your static components on static.example.org. However, if you've already set cookies on the top-level domain example.org as opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.
Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it's best to use the www subdomain and write the cookies to that subdomain.
Minimize DOM Access
tag: javascript
Accessing DOM elements with JavaScript is slow so in order to have a more responsive page, you should:
* Cache references to accessed elements
* Update nodes "offline" and then add them to the tree
* Avoid fixing layout with JavaScript
For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.
Develop Smart Event Handlers
tag: javascript
Sometimes pages feel less responsive because of too many event handlers attached to different elements of the DOM tree which are then executed too often. That's why using event delegation is a good approach. If you have 10 buttons inside a div, attach only one event handler to the div wrapper, instead of one handler for each button. Events bubble up so you'll be able to catch the event and figure out which button it originated from.
You also don't need to wait for the onload event in order to start doing something with the DOM tree. Often all you need is the element you want to access to be available in the tree. You don't have to wait for all images to be downloaded. DOMContentLoaded is the event you might consider using instead of onload, but until it's available in all browsers, you can use the YUI Event utility, which has an onAvailable method.
For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.
Choose <link> over @import
tag: css
One of the previous best practices states that CSS should be at the top in order to allow for progressive rendering.
In IE @import behaves the same as using <link> at the bottom of the page, so it's best not to use it.
Avoid Filters
tag: css
The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7. The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded. It also increases memory consumption and is applied per element, not per image, so the problem is multiplied.
The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE. If you absolutely need AlphaImageLoader, use the underscore hack _filter as to not penalize your IE7+ users.
Optimize Images
tag: images
After a designer is done with creating the images for your web page, there are still some things you can try before you FTP those images to your web server.
* You can check the GIFs and see if they are using a palette size corresponding to the number of colors in the image. Using imagemagick it's easy to check using
identify -verbose image.gif
When you see an image useing 4 colors and a 256 color "slots" in the palette, there is room for improvement.
* Try converting GIFs to PNGs and see if there is a saving. More often than not, there is. Developers often hesitate to use PNGs due to the limited support in browsers, but this is now a thing of the past. The only real problem is alpha-transparency in true color PNGs, but then again, GIFs are not true color and don't support variable transparency either. So anything a GIF can do, a palette PNG (PNG8) can do too (except for animations). This simple imagemagick command results in totally safe-to-use PNGs:
convert image.gif image.png
"All we are saying is: Give PiNG a Chance!"
* Run pngcrush (or any other PNG optimizer tool) on all your PNGs. Example:
pngcrush image.png -rem alla -reduce -brute result.png
* Run jpegtran on all your JPEGs. This tool does lossless JPEG operations such as rotation and can also be used to optimize and remove comments and other useless information (such as EXIF information) from your images.
jpegtran -copy none -optimize -perfect src.jpg dest.jpg
Optimize CSS Sprites
tag: images
* Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.
* Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.
* "Be mobile-friendly" and don't leave big gaps between the images in a sprite. This doesn't affect the file size as much but requires less memory for the user agent to decompress the image into a pixel map. 100x100 image is 10 thousand pixels, where 1000x1000 is 1 million pixels
Don't Scale Images in HTML
tag: images
Don't use a bigger image than you need just because you can set the width and height in HTML. If you need
then your image (mycat.jpg) should be 100x100px rather than a scaled down 500x500px image.
Make favicon.ico Small and Cacheable
tag: images
The favicon.ico is an image that stays in the root of your server. It's a necessary evil because even if you don't care about it the browser will still request it, so it's better not to respond with a 404 Not Found. Also since it's on the same server, cookies are sent every time it's requested. This image also interferes with the download sequence, for example in IE when you request extra components in the onload, the favicon will be downloaded before these extra components.
So to mitigate the drawbacks of having a favicon.ico make sure:
* It's small, preferably under 1K.
* Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it). You can probably safely set the Expires header a few months in the future. You can check the last modified date of your current favicon.ico to make an informed decision.
Imagemagick can help you create small favicons
Keep Components under 25K
tag: mobile
This restriction is related to the fact that iPhone won't cache components bigger than 25K. Note that this is the uncompressed size. This is where minification is important because gzip alone may not be sufficient.
For more information check "Performance Research, Part 5: iPhone Cacheability - Making it Stick" by Wayne Shea and Tenni Theurer.
Pack Components into a Multipart Document
tag: mobile
Packing components into a multipart document is like an email with attachments, it helps you fetch several components with one HTTP request (remember: HTTP requests are expensive). When you use this technique, first check if the user agent supports it (iPhone does not).
Ref: Yahoo! YDN
tag: content
80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.
One way to reduce the number of components in the page is to simplify the page's design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.
Combined files are a way to reduce the number of HTTP requests by combining all scripts into a single script, and similarly combining all CSS into a single stylesheet. Combining files is more challenging when the scripts and stylesheets vary from page to page, but making this part of your release process improves response times.
CSS Sprites are the preferred method for reducing the number of image requests. Combine your background images into a single image and use the CSS background-image and background-position properties to display the desired image segment.
Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone. Using image maps for navigation is not accessible too, so it's not recommended.
Inline images use the data: URL scheme to embed the image data in the actual page. This can increase the size of your HTML document. Combining inline images into your (cached) stylesheets is a way to reduce HTTP requests and avoid increasing the size of your pages. Inline images are not yet supported across all major browsers.
Reducing the number of HTTP requests in your page is the place to start. This is the most important guideline for improving performance for first time visitors. As described in Tenni Theurer's blog post Browser Cache Usage - Exposed!, 40-60% of daily visitors to your site come in with an empty cache. Making your page fast for these first time visitors is key to a better user experience.
Use a Content Delivery Network
tag: server
The user's proximity to your web server has an impact on response times. Deploying your content across multiple, geographically dispersed servers will make your pages load faster from the user's perspective. But where should you start?
As a first step to implementing geographically dispersed content, don't attempt to redesign your web application to work in a distributed architecture. Depending on the application, changing the architecture could include daunting tasks such as synchronizing session state and replicating database transactions across server locations. Attempts to reduce the distance between users and your content could be delayed by, or never pass, this application architecture step.
Remember that 80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc. This is the Performance Golden Rule. Rather than starting with the difficult task of redesigning your application architecture, it's better to first disperse your static content. This not only achieves a bigger reduction in response times, but it's easier thanks to content delivery networks.
A content delivery network (CDN) is a collection of web servers distributed across multiple locations to deliver content more efficiently to users. The server selected for delivering content to a specific user is typically based on a measure of network proximity. For example, the server with the fewest network hops or the server with the quickest response time is chosen.
Some large Internet companies own their own CDN, but it's cost-effective to use a CDN service provider, such as Akamai Technologies, Mirror Image Internet, or Limelight Networks. For start-up companies and private web sites, the cost of a CDN service can be prohibitive, but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times. At Yahoo!, properties that moved static content off their application web servers to a CDN improved end-user response times by 20% or more. Switching to a CDN is a relatively easy code change that will dramatically improve the speed of your web site.
Add an Expires or a Cache-Control Header
tag: server
There are two things in this rule:
* For static components: implement "Never expire" policy by setting far future Expires header
* For dynamic components: use an appropriate Cache-Control header to help the browser with conditional requests
Web page designs are getting richer and richer, which means more scripts, stylesheets, images, and Flash in the page. A first-time visitor to your page may have to make several HTTP requests, but by using the Expires header you make those components cacheable. This avoids unnecessary HTTP requests on subsequent page views. Expires headers are most often used with images, but they should be used on all components including scripts, stylesheets, and Flash components.
Browsers (and proxies) use a cache to reduce the number and size of HTTP requests, making web pages load faster. A web server uses the Expires header in the HTTP response to tell the client how long a component can be cached. This is a far future Expires header, telling the browser that this response won't be stale until April 15, 2010.
Expires: Thu, 15 Apr 2010 20:00:00 GMT
If your server is Apache, use the ExpiresDefault directive to set an expiration date relative to the current date. This example of the ExpiresDefault directive sets the Expires date 10 years out from the time of the request.
ExpiresDefault "access plus 10 years"
Keep in mind, if you use a far future Expires header you have to change the component's filename whenever the component changes. At Yahoo! we often make this step part of the build process: a version number is embedded in the component's filename, for example, yahoo_2.0.6.js.
Using a far future Expires header affects page views only after a user has already visited your site. It has no effect on the number of HTTP requests when a user visits your site for the first time and the browser's cache is empty. Therefore the impact of this performance improvement depends on how often users hit your pages with a primed cache. (A "primed cache" already contains all of the components in the page.) We measured this at Yahoo! and found the number of page views with a primed cache is 75-85%. By using a far future Expires header, you increase the number of components that are cached by the browser and re-used on subsequent page views without sending a single byte over the user's Internet connection.
Gzip Components
tag: server
The time it takes to transfer an HTTP request and response across the network can be significantly reduced by decisions made by front-end engineers. It's true that the end-user's bandwidth speed, Internet service provider, proximity to peering exchange points, etc. are beyond the control of the development team. But there are other variables that affect response times. Compression reduces response times by reducing the size of the HTTP response.
Starting with HTTP/1.1, web clients indicate support for compression with the Accept-Encoding header in the HTTP request.
Accept-Encoding: gzip, deflate
If the web server sees this header in the request, it may compress the response using one of the methods listed by the client. The web server notifies the web client of this via the Content-Encoding header in the response.
Content-Encoding: gzip
Gzip is the most popular and effective compression method at this time. It was developed by the GNU project and standardized by RFC 1952. The only other compression format you're likely to see is deflate, but it's less effective and less popular.
Gzipping generally reduces the response size by about 70%. Approximately 90% of today's Internet traffic travels through browsers that claim to support gzip. If you use Apache, the module configuring gzip depends on your version: Apache 1.3 uses mod_gzip while Apache 2.x uses mod_deflate.
There are known issues with browsers and proxies that may cause a mismatch in what the browser expects and what it receives with regard to compressed content. Fortunately, these edge cases are dwindling as the use of older browsers drops off. The Apache modules help out by adding appropriate Vary response headers automatically.
Servers choose what to gzip based on file type, but are typically too limited in what they decide to compress. Most web sites gzip their HTML documents. It's also worthwhile to gzip your scripts and stylesheets, but many web sites miss this opportunity. In fact, it's worthwhile to compress any text response including XML and JSON. Image and PDF files should not be gzipped because they are already compressed. Trying to gzip them not only wastes CPU but can potentially increase file sizes.
Gzipping as many file types as possible is an easy way to reduce page weight and accelerate the user experience.
Put Stylesheets at the Top
tag: css
While researching performance at Yahoo!, we discovered that moving stylesheets to the document HEAD makes pages appear to be loading faster. This is because putting stylesheets in the HEAD allows the page to render progressively.
Front-end engineers that care about performance want a page to load progressively; that is, we want the browser to display whatever content it has as soon as possible. This is especially important for pages with a lot of content and for users on slower Internet connections. The importance of giving users visual feedback, such as progress indicators, has been well researched and documented. In our case the HTML page is the progress indicator! When the browser loads the page progressively the header, the navigation bar, the logo at the top, etc. all serve as visual feedback for the user who is waiting for the page. This improves the overall user experience.
The problem with putting stylesheets near the bottom of the document is that it prohibits progressive rendering in many browsers, including Internet Explorer. These browsers block rendering to avoid having to redraw elements of the page if their styles change. The user is stuck viewing a blank white page.
The HTML specification clearly states that stylesheets are to be included in the HEAD of the page: "Unlike A, [LINK] may only appear in the HEAD section of a document, although it may appear any number of times." Neither of the alternatives, the blank white screen or flash of unstyled content, are worth the risk. The optimal solution is to follow the HTML specification and load your stylesheets in the document HEAD.
Put Scripts at the Bottom
tag: javascript
The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won't start any other downloads, even on different hostnames.
In some situations it's not easy to move scripts to the bottom. If, for example, the script uses document.write to insert part of the page's content, it can't be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.
An alternative suggestion that often comes up is to use deferred scripts. The DEFER attribute indicates that the script does not contain document.write, and is a clue to browsers that they can continue rendering. Unfortunately, Firefox doesn't support the DEFER attribute. In Internet Explorer, the script may be deferred, but not as much as desired. If a script can be deferred, it can also be moved to the bottom of the page. That will make your web pages load faster.
Avoid CSS Expressions
tag: css
CSS expressions are a powerful (and dangerous) way to set CSS properties dynamically. They're supported in Internet Explorer, starting with version 5. As an example, the background color could be set to alternate every hour using CSS expressions.
background-color: expression( (new Date()).getHours()%2 ? "#B8D4FF" : "#F08A00" );
As shown here, the expression method accepts a JavaScript expression. The CSS property is set to the result of evaluating the JavaScript expression. The expression method is ignored by other browsers, so it is useful for setting properties in Internet Explorer needed to create a consistent experience across browsers.
The problem with expressions is that they are evaluated more frequently than most people expect. Not only are they evaluated when the page is rendered and resized, but also when the page is scrolled and even when the user moves the mouse over the page. Adding a counter to the CSS expression allows us to keep track of when and how often a CSS expression is evaluated. Moving the mouse around the page can easily generate more than 10,000 evaluations.
One way to reduce the number of times your CSS expression is evaluated is to use one-time expressions, where the first time the expression is evaluated it sets the style property to an explicit value, which replaces the CSS expression. If the style property must be set dynamically throughout the life of the page, using event handlers instead of CSS expressions is an alternative approach. If you must use CSS expressions, remember that they may be evaluated thousands of times and could affect the performance of your page.
Make JavaScript and CSS External
tag: javascript, css
Many of these performance rules deal with how external components are managed. However, before these considerations arise you should ask a more basic question: Should JavaScript and CSS be contained in external files, or inlined in the page itself?
Using external files in the real world generally produces faster pages because the JavaScript and CSS files are cached by the browser. JavaScript and CSS that are inlined in HTML documents get downloaded every time the HTML document is requested. This reduces the number of HTTP requests that are needed, but increases the size of the HTML document. On the other hand, if the JavaScript and CSS are in external files cached by the browser, the size of the HTML document is reduced without increasing the number of HTTP requests.
The key factor, then, is the frequency with which external JavaScript and CSS components are cached relative to the number of HTML documents requested. This factor, although difficult to quantify, can be gauged using various metrics. If users on your site have multiple page views per session and many of your pages re-use the same scripts and stylesheets, there is a greater potential benefit from cached external files.
Many web sites fall in the middle of these metrics. For these sites, the best solution generally is to deploy the JavaScript and CSS as external files. The only exception where inlining is preferable is with home pages, such as Yahoo!'s front page and My Yahoo!. Home pages that have few (perhaps only one) page view per session may find that inlining JavaScript and CSS results in faster end-user response times.
For front pages that are typically the first of many page views, there are techniques that leverage the reduction of HTTP requests that inlining provides, as well as the caching benefits achieved through using external files. One such technique is to inline JavaScript and CSS in the front page, but dynamically download the external files after the page has finished loading. Subsequent pages would reference the external files that should already be in the browser's cache.
Reduce DNS Lookups
tag: content
The Domain Name System (DNS) maps hostnames to IP addresses, just as phonebooks map people's names to their phone numbers. When you type www.yahoo.com into your browser, a DNS resolver contacted by the browser returns that server's IP address. DNS has a cost. It typically takes 20-120 milliseconds for DNS to lookup the IP address for a given hostname. The browser can't download anything from this hostname until the DNS lookup is completed.
DNS lookups are cached for better performance. This caching can occur on a special caching server, maintained by the user's ISP or local area network, but there is also caching that occurs on the individual user's computer. The DNS information remains in the operating system's DNS cache (the "DNS Client service" on Microsoft Windows). Most browsers have their own caches, separate from the operating system's cache. As long as the browser keeps a DNS record in its own cache, it doesn't bother the operating system with a request for the record.
Internet Explorer caches DNS lookups for 30 minutes by default, as specified by the DnsCacheTimeout registry setting. Firefox caches DNS lookups for 1 minute, controlled by the network.dnsCacheExpiration configuration setting. (Fasterfox changes this to 1 hour.)
When the client's DNS cache is empty (for both the browser and the operating system), the number of DNS lookups is equal to the number of unique hostnames in the web page. This includes the hostnames used in the page's URL, images, script files, stylesheets, Flash objects, etc. Reducing the number of unique hostnames reduces the number of DNS lookups.
Reducing the number of unique hostnames has the potential to reduce the amount of parallel downloading that takes place in the page. Avoiding DNS lookups cuts response times, but reducing parallel downloads may increase response times. My guideline is to split these components across at least two but no more than four hostnames. This results in a good compromise between reducing DNS lookups and allowing a high degree of parallel downloads.
Minify JavaScript and CSS
tag: javascript, css
Minification is the practice of removing unnecessary characters from code to reduce its size thereby improving load times. When code is minified all comments are removed, as well as unneeded white space characters (space, newline, and tab). In the case of JavaScript, this improves response time performance because the size of the downloaded file is reduced. Two popular tools for minifying JavaScript code are JSMin and YUI Compressor. The YUI compressor can also minify CSS.
Obfuscation is an alternative optimization that can be applied to source code. It's more complex than minification and thus more likely to generate bugs as a result of the obfuscation step itself. In a survey of ten top U.S. web sites, minification achieved a 21% size reduction versus 25% for obfuscation. Although obfuscation has a higher size reduction, minifying JavaScript is less risky.
In addition to minifying external scripts and styles, inlined <script> and <style> blocks can and should also be minified. Even if you gzip your scripts and styles, minifying them will still reduce the size by 5% or more. As the use and size of JavaScript and CSS increases, so will the savings gained by minifying your code.
Avoid Redirects
tag: content
Redirects are accomplished using the 301 and 302 status codes. Here's an example of the HTTP headers in a 301 response:
HTTP/1.1 301 Moved Permanently
Location: http://example.com/newuri
Content-Type: text/html
The browser automatically takes the user to the URL specified in the Location field. All the information necessary for a redirect is in the headers. The body of the response is typically empty. Despite their names, neither a 301 nor a 302 response is cached in practice unless additional headers, such as Expires or Cache-Control, indicate it should be. The meta refresh tag and JavaScript are other ways to direct users to a different URL, but if you must do a redirect, the preferred technique is to use the standard 3xx HTTP status codes, primarily to ensure the back button works correctly.
The main thing to remember is that redirects slow down the user experience. Inserting a redirect between the user and the HTML document delays everything in the page since nothing in the page can be rendered and no components can start being downloaded until the HTML document has arrived.
One of the most wasteful redirects happens frequently and web developers are generally not aware of it. It occurs when a trailing slash (/) is missing from a URL that should otherwise have one. For example, going to http://astrology.yahoo.com/astrology results in a 301 response containing a redirect to http://astrology.yahoo.com/astrology/ (notice the added trailing slash). This is fixed in Apache by using Alias or mod_rewrite, or the DirectorySlash directive if you're using Apache handlers.
Connecting an old web site to a new one is another common use for redirects. Others include connecting different parts of a website and directing the user based on certain conditions (type of browser, type of user account, etc.). Using a redirect to connect two web sites is simple and requires little additional coding. Although using redirects in these situations reduces the complexity for developers, it degrades the user experience. Alternatives for this use of redirects include using Alias and mod_rewrite if the two code paths are hosted on the same server. If a domain name change is the cause of using redirects, an alternative is to create a CNAME (a DNS record that creates an alias pointing from one domain name to another) in combination with Alias or mod_rewrite.
Remove Duplicate Scripts
tag: javascript
It hurts performance to include the same JavaScript file twice in one page. This isn't as unusual as you might think. A review of the ten top U.S. web sites shows that two of them contain a duplicated script. Two main factors increase the odds of a script being duplicated in a single web page: team size and number of scripts. When it does happen, duplicate scripts hurt performance by creating unnecessary HTTP requests and wasted JavaScript execution.
Unnecessary HTTP requests happen in Internet Explorer, but not in Firefox. In Internet Explorer, if an external script is included twice and is not cacheable, it generates two HTTP requests during page loading. Even if the script is cacheable, extra HTTP requests occur when the user reloads the page.
In addition to generating wasteful HTTP requests, time is wasted evaluating the script multiple times. This redundant JavaScript execution happens in both Firefox and Internet Explorer, regardless of whether the script is cacheable.
One way to avoid accidentally including the same script twice is to implement a script management module in your templating system. The typical way to include a script is to use the SCRIPT tag in your HTML page.
An alternative in PHP would be to create a function called insertScript.
In addition to preventing the same script from being inserted multiple times, this function could handle other issues with scripts, such as dependency checking and adding version numbers to script filenames to support far future Expires headers.
Configure ETags
tag: server
Entity tags (ETags) are a mechanism that web servers and browsers use to determine whether the component in the browser's cache matches the one on the origin server. (An "entity" is another word a "component": images, scripts, stylesheets, etc.) ETags were added to provide a mechanism for validating entities that is more flexible than the last-modified date. An ETag is a string that uniquely identifies a specific version of a component. The only format constraints are that the string be quoted. The origin server specifies the component's ETag using the ETag response header.
HTTP/1.1 200 OK
Last-Modified: Tue, 12 Dec 2006 03:03:59 GMT
ETag: "10c24bc-4ab-457e1c1f"
Content-Length: 12195
Later, if the browser has to validate a component, it uses the If-None-Match header to pass the ETag back to the origin server. If the ETags match, a 304 status code is returned reducing the response by 12195 bytes for this example.
GET /i/yahoo.gif HTTP/1.1
Host: us.yimg.com
If-Modified-Since: Tue, 12 Dec 2006 03:03:59 GMT
If-None-Match: "10c24bc-4ab-457e1c1f"
HTTP/1.1 304 Not Modified
The problem with ETags is that they typically are constructed using attributes that make them unique to a specific server hosting a site. ETags won't match when a browser gets the original component from one server and later tries to validate that component on a different server, a situation that is all too common on Web sites that use a cluster of servers to handle requests. By default, both Apache and IIS embed data in the ETag that dramatically reduces the odds of the validity test succeeding on web sites with multiple servers.
The ETag format for Apache 1.3 and 2.x is inode-size-timestamp. Although a given file may reside in the same directory across multiple servers, and have the same file size, permissions, timestamp, etc., its inode is different from one server to the next.
IIS 5.0 and 6.0 have a similar issue with ETags. The format for ETags on IIS is Filetimestamp:ChangeNumber. A ChangeNumber is a counter used to track configuration changes to IIS. It's unlikely that the ChangeNumber is the same across all IIS servers behind a web site.
The end result is ETags generated by Apache and IIS for the exact same component won't match from one server to another. If the ETags don't match, the user doesn't receive the small, fast 304 response that ETags were designed for; instead, they'll get a normal 200 response along with all the data for the component. If you host your web site on just one server, this isn't a problem. But if you have multiple servers hosting your web site, and you're using Apache or IIS with the default ETag configuration, your users are getting slower pages, your servers have a higher load, you're consuming greater bandwidth, and proxies aren't caching your content efficiently. Even if your components have a far future Expires header, a conditional GET request is still made whenever the user hits Reload or Refresh.
If you're not taking advantage of the flexible validation model that ETags provide, it's better to just remove the ETag altogether. The Last-Modified header validates based on the component's timestamp. And removing the ETag reduces the size of the HTTP headers in both the response and subsequent requests. This Microsoft Support article describes how to remove ETags. In Apache, this is done by simply adding the following line to your Apache configuration file:
FileETag none
Make Ajax Cacheable
tag: content
One of the cited benefits of Ajax is that it provides instantaneous feedback to the user because it requests information asynchronously from the backend web server. However, using Ajax is no guarantee that the user won't be twiddling his thumbs waiting for those asynchronous JavaScript and XML responses to return. In many applications, whether or not the user is kept waiting depends on how Ajax is used. For example, in a web-based email client the user will be kept waiting for the results of an Ajax request to find all the email messages that match their search criteria. It's important to remember that "asynchronous" does not imply "instantaneous".
To improve performance, it's important to optimize these Ajax responses. The most important way to improve the performance of Ajax is to make the responses cacheable, as discussed in Add an Expires or a Cache-Control Header. Some of the other rules also apply to Ajax:
* Gzip Components
* Reduce DNS Lookups
* Minify JavaScript
* Avoid Redirects
* Configure ETags
Let's look at an example. A Web 2.0 email client might use Ajax to download the user's address book for autocompletion. If the user hasn't modified her address book since the last time she used the email web app, the previous address book response could be read from cache if that Ajax response was made cacheable with a future Expires or Cache-Control header. The browser must be informed when to use a previously cached address book response versus requesting a new one. This could be done by adding a timestamp to the address book Ajax URL indicating the last time the user modified her address book, for example, &t=1190241612. If the address book hasn't been modified since the last download, the timestamp will be the same and the address book will be read from the browser's cache eliminating an extra HTTP roundtrip. If the user has modified her address book, the timestamp ensures the new URL doesn't match the cached response, and the browser will request the updated address book entries.
Even though your Ajax responses are created dynamically, and might only be applicable to a single user, they can still be cached. Doing so will make your Web 2.0 apps faster.
Flush the Buffer Early
tag: server
When users request a page, it can take anywhere from 200 to 500ms for the backend server to stitch together the HTML page. During this time, the browser is idle as it waits for the data to arrive. In PHP you have the function flush(). It allows you to send your partially ready HTML response to the browser so that the browser can start fetching components while your backend is busy with the rest of the HTML page. The benefit is mainly seen on busy backends or light frontends.
A good place to consider flushing is right after the HEAD because the HTML for the head is usually easier to produce and it allows you to include any CSS and JavaScript files for the browser to start fetching in parallel while the backend is still processing.
Example:
... <!-- css, js -->
</head>
<?php flush(); ?>
<body>
... <!-- content -->
Yahoo! search pioneered research and real user testing to prove the benefits of using this technique.
Use GET for AJAX Requests
tag: server
The Yahoo! Mail team found that when using XMLHttpRequest, POST is implemented in the browsers as a two-step process: sending the headers first, then sending data. So it's best to use GET, which only takes one TCP packet to send (unless you have a lot of cookies). The maximum URL length in IE is 2K, so if you send more than 2K data you might not be able to use GET.
An interesting side affect is that POST without actually posting any data behaves like GET. Based on the HTTP specs, GET is meant for retrieving information, so it makes sense (semantically) to use GET when you're only requesting data, as opposed to sending data to be stored server-side.
Post-load Components
tag: content
You can take a closer look at your page and ask yourself: "What's absolutely required in order to render the page initially?". The rest of the content and components can wait.
JavaScript is an ideal candidate for splitting before and after the onload event. For example if you have JavaScript code and libraries that do drag and drop and animations, those can wait, because dragging elements on the page comes after the initial rendering. Other places to look for candidates for post-loading include hidden content (content that appears after a user action) and images below the fold.
Tools to help you out in your effort: YUI Image Loader allows you to delay images below the fold and the YUI Get utility is an easy way to include JS and CSS on the fly. For an example in the wild take a look at Yahoo! Home Page with Firebug's Net Panel turned on.
It's good when the performance goals are inline with other web development best practices. In this case, the idea of progressive enhancement tells us that JavaScript, when supported, can improve the user experience but you have to make sure the page works even without JavaScript. So after you've made sure the page works fine, you can enhance it with some post-loaded scripts that give you more bells and whistles such as drag and drop and animations.
Preload Components
tag: content
Preload may look like the opposite of post-load, but it actually has a different goal. By preloading components you can take advantage of the time the browser is idle and request components (like images, styles and scripts) you'll need in the future. This way when the user visits the next page, you could have most of the components already in the cache and your page will load much faster for the user.
There are actually several types of preloading:
* Unconditional preload - as soon as onload fires, you go ahead and fetch some extra components. Check google.com for an example of how a sprite image is requested onload. This sprite image is not needed on the google.com homepage, but it is needed on the consecutive search result page.
* Conditional preload - based on a user action you make an educated guess where the user is headed next and preload accordingly. On search.yahoo.com you can see how some extra components are requested after you start typing in the input box.
* Anticipated preload - preload in advance before launching a redesign. It often happens after a redesign that you hear: "The new site is cool, but it's slower than before". Part of the problem could be that the users were visiting your old site with a full cache, but the new one is always an empty cache experience. You can mitigate this side effect by preloading some components before you even launched the redesign. Your old site can use the time the browser is idle and request images and scripts that will be used by the new site
Reduce the Number of DOM Elements
tag: content
A complex page means more bytes to download and it also means slower DOM access in JavaScript. It makes a difference if you loop through 500 or 5000 DOM elements on the page when you want to add an event handler for example.
A high number of DOM elements can be a symptom that there's something that should be improved with the markup of the page without necessarily removing content. Are you using nested tables for layout purposes? Are you throwing in more <div>s only to fix layout issues? Maybe there's a better and more semantically correct way to do your markup.
A great help with layouts are the YUI CSS utilities: grids.css can help you with the overall layout, fonts.css and reset.css can help you strip away the browser's defaults formatting. This is a chance to start fresh and think about your markup, for example use <div>s only when it makes sense semantically, and not because it renders a new line.
The number of DOM elements is easy to test, just type in Firebug's console:
document.getElementsByTagName('*').length
And how many DOM elements are too many? Check other similar pages that have good markup. For example the Yahoo! Home Page is a pretty busy page and still under 700 elements (HTML tags).
Split Components Across Domains
tag: content
Splitting components allows you to maximize parallel downloads. Make sure you're using not more than 2-4 domains because of the DNS lookup penalty. For example, you can host your HTML and dynamic content on www.example.org and split static components between static1.example.org and static2.example.org
Minimize the Number of iframes
tag: content
Iframes allow an HTML document to be inserted in the parent document. It's important to understand how iframes work so they can be used effectively.
<iframe> pros:
* Helps with slow third-party content like badges and ads
* Security sandbox
* Download scripts in parallel
<iframe> cons:
* Costly even if blank
* Blocks page onload
* Non-semantic
No 404s
tag: content
HTTP requests are expensive so making an HTTP request and getting a useless response (i.e. 404 Not Found) is totally unnecessary and will slow down the user experience without any benefit.
Some sites have helpful 404s "Did you mean X?", which is great for the user experience but also wastes server resources (like database, etc). Particularly bad is when the link to an external JavaScript is wrong and the result is a 404. First, this download will block parallel downloads. Next the browser may try to parse the 404 response body as if it were JavaScript code, trying to find something usable in it.
Reduce Cookie Size
tag: cookie
HTTP cookies are used for a variety of reasons such as authentication and personalization. Information about cookies is exchanged in the HTTP headers between web servers and browsers. It's important to keep the size of cookies as low as possible to minimize the impact on the user's response time.
For more information check "When the Cookie Crumbles" by Tenni Theurer and Patty Chi. The take-home of this research:
* Eliminate unnecessary cookies
* Keep cookie sizes as low as possible to minimize the impact on the user response time
* Be mindful of setting cookies at the appropriate domain level so other sub-domains are not affected
* Set an Expires date appropriately. An earlier Expires date or none removes the cookie sooner, improving the user response time
Use Cookie-free Domains for Components
tag: cookie
When the browser makes a request for a static image and sends cookies together with the request, the server doesn't have any use for those cookies. So they only create network traffic for no good reason. You should make sure static components are requested with cookie-free requests. Create a subdomain and host all your static components there.
If your domain is www.example.org, you can host your static components on static.example.org. However, if you've already set cookies on the top-level domain example.org as opposed to www.example.org, then all the requests to static.example.org will include those cookies. In this case, you can buy a whole new domain, host your static components there, and keep this domain cookie-free. Yahoo! uses yimg.com, YouTube uses ytimg.com, Amazon uses images-amazon.com and so on.
Another benefit of hosting static components on a cookie-free domain is that some proxies might refuse to cache the components that are requested with cookies. On a related note, if you wonder if you should use example.org or www.example.org for your home page, consider the cookie impact. Omitting www leaves you no choice but to write cookies to *.example.org, so for performance reasons it's best to use the www subdomain and write the cookies to that subdomain.
Minimize DOM Access
tag: javascript
Accessing DOM elements with JavaScript is slow so in order to have a more responsive page, you should:
* Cache references to accessed elements
* Update nodes "offline" and then add them to the tree
* Avoid fixing layout with JavaScript
For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.
Develop Smart Event Handlers
tag: javascript
Sometimes pages feel less responsive because of too many event handlers attached to different elements of the DOM tree which are then executed too often. That's why using event delegation is a good approach. If you have 10 buttons inside a div, attach only one event handler to the div wrapper, instead of one handler for each button. Events bubble up so you'll be able to catch the event and figure out which button it originated from.
You also don't need to wait for the onload event in order to start doing something with the DOM tree. Often all you need is the element you want to access to be available in the tree. You don't have to wait for all images to be downloaded. DOMContentLoaded is the event you might consider using instead of onload, but until it's available in all browsers, you can use the YUI Event utility, which has an onAvailable method.
For more information check the YUI theatre's "High Performance Ajax Applications" by Julien Lecomte.
Choose <link> over @import
tag: css
One of the previous best practices states that CSS should be at the top in order to allow for progressive rendering.
In IE @import behaves the same as using <link> at the bottom of the page, so it's best not to use it.
Avoid Filters
tag: css
The IE-proprietary AlphaImageLoader filter aims to fix a problem with semi-transparent true color PNGs in IE versions < 7. The problem with this filter is that it blocks rendering and freezes the browser while the image is being downloaded. It also increases memory consumption and is applied per element, not per image, so the problem is multiplied.
The best approach is to avoid AlphaImageLoader completely and use gracefully degrading PNG8 instead, which are fine in IE. If you absolutely need AlphaImageLoader, use the underscore hack _filter as to not penalize your IE7+ users.
Optimize Images
tag: images
After a designer is done with creating the images for your web page, there are still some things you can try before you FTP those images to your web server.
* You can check the GIFs and see if they are using a palette size corresponding to the number of colors in the image. Using imagemagick it's easy to check using
identify -verbose image.gif
When you see an image useing 4 colors and a 256 color "slots" in the palette, there is room for improvement.
* Try converting GIFs to PNGs and see if there is a saving. More often than not, there is. Developers often hesitate to use PNGs due to the limited support in browsers, but this is now a thing of the past. The only real problem is alpha-transparency in true color PNGs, but then again, GIFs are not true color and don't support variable transparency either. So anything a GIF can do, a palette PNG (PNG8) can do too (except for animations). This simple imagemagick command results in totally safe-to-use PNGs:
convert image.gif image.png
"All we are saying is: Give PiNG a Chance!"
* Run pngcrush (or any other PNG optimizer tool) on all your PNGs. Example:
pngcrush image.png -rem alla -reduce -brute result.png
* Run jpegtran on all your JPEGs. This tool does lossless JPEG operations such as rotation and can also be used to optimize and remove comments and other useless information (such as EXIF information) from your images.
jpegtran -copy none -optimize -perfect src.jpg dest.jpg
Optimize CSS Sprites
tag: images
* Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.
* Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.
* "Be mobile-friendly" and don't leave big gaps between the images in a sprite. This doesn't affect the file size as much but requires less memory for the user agent to decompress the image into a pixel map. 100x100 image is 10 thousand pixels, where 1000x1000 is 1 million pixels
Don't Scale Images in HTML
tag: images
Don't use a bigger image than you need just because you can set the width and height in HTML. If you need
then your image (mycat.jpg) should be 100x100px rather than a scaled down 500x500px image.
Make favicon.ico Small and Cacheable
tag: images
The favicon.ico is an image that stays in the root of your server. It's a necessary evil because even if you don't care about it the browser will still request it, so it's better not to respond with a 404 Not Found. Also since it's on the same server, cookies are sent every time it's requested. This image also interferes with the download sequence, for example in IE when you request extra components in the onload, the favicon will be downloaded before these extra components.
So to mitigate the drawbacks of having a favicon.ico make sure:
* It's small, preferably under 1K.
* Set Expires header with what you feel comfortable (since you cannot rename it if you decide to change it). You can probably safely set the Expires header a few months in the future. You can check the last modified date of your current favicon.ico to make an informed decision.
Imagemagick can help you create small favicons
Keep Components under 25K
tag: mobile
This restriction is related to the fact that iPhone won't cache components bigger than 25K. Note that this is the uncompressed size. This is where minification is important because gzip alone may not be sufficient.
For more information check "Performance Research, Part 5: iPhone Cacheability - Making it Stick" by Wayne Shea and Tenni Theurer.
Pack Components into a Multipart Document
tag: mobile
Packing components into a multipart document is like an email with attachments, it helps you fetch several components with one HTTP request (remember: HTTP requests are expensive). When you use this technique, first check if the user agent supports it (iPhone does not).
Ref: Yahoo! YDN
Sunday, January 4, 2009
40 Tips for optimizing your php code
1. If a method can be static, declare it static. Speed improvement is by a factor of 4.
2. echo is faster than print.
3. Use echo's multiple parameters instead of string concatenation.
4. Set the maxvalue for your for-loops before and not in the loop.
5. Unset your variables to free memory, especially large arrays.
6. Avoid magic like __get, __set, __autoload
7. require_once() is expensive
8. Use full paths in includes and requires, less time spent on resolving the OS paths.
9. If you need to find out the time when the script started executing, $_SERVER[’REQUEST_TIME’] is preferred to time()
10. See if you can use strncasecmp, strpbrk and stripos instead of regex
11. str_replace is faster than preg_replace, but strtr is faster than str_replace by a factor of 4
12. If the function, such as string replacement function, accepts both arrays and single characters as arguments, and if your argument list is not too long, consider writing a few redundant replacement statements, passing one character at a time, instead of one line of code that accepts arrays as search and replace arguments.
13. It's better to use switch statements than multi if, else if, statements.
14. Error suppression with @ is very slow.
15. Turn on apache's mod_deflate
16. Close your database connections when you're done with them
17. $row[’id’] is 7 times faster than $row[id]
18. Error messages are expensive
19. Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time.
20. Incrementing a local variable in a method is the fastest. Nearly the same as calling a local variable in a function.
21. Incrementing a global variable is 2 times slow than a local var.
22. Incrementing an object property (eg. $this->prop++) is 3 times slower than a local variable.
23. Incrementing an undefined local variable is 9-10 times slower than a pre-initialized one.
24. Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var). PHP probably does a check to see if the global exists.
25. Method invocation appears to be independent of the number of methods defined in the class because I added 10 more methods to the test class (before and after the test method) with no change in performance.
26. Methods in derived classes run faster than ones defined in the base class.
27. A function call with one parameter and an empty function body takes about the same time as doing 7-8 $localvar++ operations. A similar method call is of course about 15 $localvar++ operations.
28. Surrounding your string by ' instead of " will make things interpret a little faster since php looks for variables inside "..." but not inside '...'. Of course you can only do this when you don't need to have variables in the string.
29. When echoing strings it's faster to separate them by comma instead of dot. Note: This only works with echo, which is a function that can take several strings as arguments.
30. A PHP script will be served at least 2-10 times slower than a static HTML page by Apache. Try to use more static HTML pages and fewer scripts.
31. Your PHP scripts are recompiled every time unless the scripts are cached. Install a PHP caching product to typically increase performance by 25-100% by removing compile times.
32. Cache as much as possible. Use memcached - memcached is a high-performance memory object caching system intended to speed up dynamic web applications by alleviating database load. OP code caches are useful so that your script does not have to be compiled on every request
33. When working with strings and you need to check that the string is either of a certain length you'd understandably would want to use the strlen() function. This function is pretty quick since it's operation does not perform any calculation but merely return the already known length of a string available in the zval structure (internal C struct used to store variables in PHP). However because strlen() is a function it is still somewhat slow because the function call requires several operations such as lowercase & hashtable lookup followed by the execution of said function. In some instance you can improve the speed of your code by using an isset() trick.
Ex.
if (strlen($foo) < 5) { echo "Foo is too short"; }
vs.
if (!isset($foo{5})) { echo "Foo is too short"; }
Calling isset() happens to be faster then strlen() because unlike strlen(), isset() is a language construct and not a function meaning that it's execution does not require function lookups and lowercase. This means you have virtually no overhead on top of the actual code that determines the string's length.
34. When incrementing or decrementing the value of the variable $i++ happens to be a tad slower then ++$i. This is something PHP specific and does not apply to other languages, so don't go modifying your C or Java code thinking it'll suddenly become faster, it won't. ++$i happens to be faster in PHP because instead of 4 opcodes used for $i++ you only need 3. Post incrementation actually causes in the creation of a temporary var that is then incremented. While pre-incrementation increases the original value directly. This is one of the optimization that opcode optimized like Zend's PHP optimizer. It is a still a good idea to keep in mind since not all opcode optimizers perform this optimization and there are plenty of ISPs and servers running without an opcode optimizer.
35. Not everything has to be OOP, often it is too much overhead, each method and object call consumes a lot of memory.
36. Do not implement every data structure as a class, arrays are useful, too
37. Don't split methods too much, think, which code you will really re-use
38. You can always split the code of a method later, when needed
39. Make use of the countless predefined functions
40. If you have very time consuming functions in your code, consider writing them as C extensions
41. Profile your code. A profiler shows you, which parts of your code consumes how many time. The Xdebug debugger already contains a profiler. Profiling shows you the bottlenecks in overview
42. mod_gzip which is available as an Apache module compresses your data on the fly and can reduce the data to transfer up to 80%
43. Excellent Article about optimizing php by John Lim
2. echo is faster than print.
3. Use echo's multiple parameters instead of string concatenation.
4. Set the maxvalue for your for-loops before and not in the loop.
5. Unset your variables to free memory, especially large arrays.
6. Avoid magic like __get, __set, __autoload
7. require_once() is expensive
8. Use full paths in includes and requires, less time spent on resolving the OS paths.
9. If you need to find out the time when the script started executing, $_SERVER[’REQUEST_TIME’] is preferred to time()
10. See if you can use strncasecmp, strpbrk and stripos instead of regex
11. str_replace is faster than preg_replace, but strtr is faster than str_replace by a factor of 4
12. If the function, such as string replacement function, accepts both arrays and single characters as arguments, and if your argument list is not too long, consider writing a few redundant replacement statements, passing one character at a time, instead of one line of code that accepts arrays as search and replace arguments.
13. It's better to use switch statements than multi if, else if, statements.
14. Error suppression with @ is very slow.
15. Turn on apache's mod_deflate
16. Close your database connections when you're done with them
17. $row[’id’] is 7 times faster than $row[id]
18. Error messages are expensive
19. Do not use functions inside of for loop, such as for ($x=0; $x < count($array); $x) The count() function gets called each time.
20. Incrementing a local variable in a method is the fastest. Nearly the same as calling a local variable in a function.
21. Incrementing a global variable is 2 times slow than a local var.
22. Incrementing an object property (eg. $this->prop++) is 3 times slower than a local variable.
23. Incrementing an undefined local variable is 9-10 times slower than a pre-initialized one.
24. Just declaring a global variable without using it in a function also slows things down (by about the same amount as incrementing a local var). PHP probably does a check to see if the global exists.
25. Method invocation appears to be independent of the number of methods defined in the class because I added 10 more methods to the test class (before and after the test method) with no change in performance.
26. Methods in derived classes run faster than ones defined in the base class.
27. A function call with one parameter and an empty function body takes about the same time as doing 7-8 $localvar++ operations. A similar method call is of course about 15 $localvar++ operations.
28. Surrounding your string by ' instead of " will make things interpret a little faster since php looks for variables inside "..." but not inside '...'. Of course you can only do this when you don't need to have variables in the string.
29. When echoing strings it's faster to separate them by comma instead of dot. Note: This only works with echo, which is a function that can take several strings as arguments.
30. A PHP script will be served at least 2-10 times slower than a static HTML page by Apache. Try to use more static HTML pages and fewer scripts.
31. Your PHP scripts are recompiled every time unless the scripts are cached. Install a PHP caching product to typically increase performance by 25-100% by removing compile times.
32. Cache as much as possible. Use memcached - memcached is a high-performance memory object caching system intended to speed up dynamic web applications by alleviating database load. OP code caches are useful so that your script does not have to be compiled on every request
33. When working with strings and you need to check that the string is either of a certain length you'd understandably would want to use the strlen() function. This function is pretty quick since it's operation does not perform any calculation but merely return the already known length of a string available in the zval structure (internal C struct used to store variables in PHP). However because strlen() is a function it is still somewhat slow because the function call requires several operations such as lowercase & hashtable lookup followed by the execution of said function. In some instance you can improve the speed of your code by using an isset() trick.
Ex.
if (strlen($foo) < 5) { echo "Foo is too short"; }
vs.
if (!isset($foo{5})) { echo "Foo is too short"; }
Calling isset() happens to be faster then strlen() because unlike strlen(), isset() is a language construct and not a function meaning that it's execution does not require function lookups and lowercase. This means you have virtually no overhead on top of the actual code that determines the string's length.
34. When incrementing or decrementing the value of the variable $i++ happens to be a tad slower then ++$i. This is something PHP specific and does not apply to other languages, so don't go modifying your C or Java code thinking it'll suddenly become faster, it won't. ++$i happens to be faster in PHP because instead of 4 opcodes used for $i++ you only need 3. Post incrementation actually causes in the creation of a temporary var that is then incremented. While pre-incrementation increases the original value directly. This is one of the optimization that opcode optimized like Zend's PHP optimizer. It is a still a good idea to keep in mind since not all opcode optimizers perform this optimization and there are plenty of ISPs and servers running without an opcode optimizer.
35. Not everything has to be OOP, often it is too much overhead, each method and object call consumes a lot of memory.
36. Do not implement every data structure as a class, arrays are useful, too
37. Don't split methods too much, think, which code you will really re-use
38. You can always split the code of a method later, when needed
39. Make use of the countless predefined functions
40. If you have very time consuming functions in your code, consider writing them as C extensions
41. Profile your code. A profiler shows you, which parts of your code consumes how many time. The Xdebug debugger already contains a profiler. Profiling shows you the bottlenecks in overview
42. mod_gzip which is available as an Apache module compresses your data on the fly and can reduce the data to transfer up to 80%
43. Excellent Article about optimizing php by John Lim
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