Tuning web performance
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This document discusses techniques for optimizing web performance from a frontend perspective. It covers development tools for analyzing performance, common issues that impact performance like long response times and unnecessary requests, and optimization strategies like minifying files, using content delivery networks, browser caching, and improving JavaScript efficiency. The document provides many specific examples and recommendations for optimizing images, CSS, HTML, and JavaScript to improve frontend performance.
![HTTP Reuqest Example
$ telnet ajax.googleapis.com 80
Trying 74.125.153.95...
Connected to googleapis-ajax.l.google.com.
Escape character is '^]'.
GET /ajax/libs/jquery/1.4.2/jquery.min.js HTTP/1.1
Host: ajax.googleapis.com
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; zh-TW; rv:1.9.2)
Gecko/20100115 Firefox/3.6 GTB7.0
Accept-Encoding: gzip,deflate
HTTP/1.1 200 OK
Content-Type: text/javascript; charset=UTF-8
Last-Modified: Mon, 15 Feb 2010 23:30:12 GMT
Date: Mon, 15 Mar 2010 08:39:18 GMT
Expires: Tue, 15 Mar 2011 08:39:18 GMT
Vary: Accept-Encoding
X-Content-Type-Options: nosniff
Server: sffe
Content-Encoding: gzip
Cache-Control: public, max-age=31536000
Age: 2497
Content-Length: 24678
X-XSS-Protection: 0
;iw?F???+??m?@ə???v?I։/M???6???????$e???...](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-13-320.jpg)
![HTTP Compression
In Apache httpd server, use mod_gzip (httpd 1.3) or
mod_deflate (httpd 2.x).
[mod_deflate]
AddOutputFilterByType DEFLATE text/html text/css
application/x-javascript
Problems:
Proxy may cache uncompressed content
Add Vary: Accept-Encoding header
IE6 bug: Q312496, Q313712](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-19-320.jpg)
![Using Last-Modified Headers
Use Last-Modified header to tell the browser the last modified
time of the resource.
[request] [request]
GET /foo/bar.css HTTP/1.1 GET /foo/bar.css HTTP/1.1
.... ...
If-Modified-Since: Thu, 25 Mar 2010
[response] 10:00:00 GMT
HTTP/1.1 200 OK ...
Content-Type: text/css
Last-Modified: Thu, 25 Mar 2010 10: [response]
00:00 GMT+8 HTTP/1.1 304 Not Modified
.... ...
(empty response body)](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-23-320.jpg)
![Efficient JavaScript Tips
Using className instead of modifying style attributes of a DOM
element.
[bad
]
var foo = document.getElementById('foo');
foo.style.color = '#f00';
foo.style.fontWeight = 'bold';
[good]
.highlight {
color: #f00;
font-weight: bold;
}
foo.className = 'highlight';](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-37-320.jpg)
![Efficient JavaScript Tips (con'd)
Appending a newly-created DOM element after modifying its
attributes. (avoid reflows)
[bad]
var foo = document.createElement('div');
document.body.appendChild(foo);
foo.innerHTML = 'Hello, world';
foo.className = 'hello';
[good]
var foo = document.createElement('div');
foo.innerHTML = 'Hello, world';
foo.className = 'hello';
document.body.appendChild(foo);](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-38-320.jpg)
![Efficient JavaScript Tips
Using document fragment to create new contents.
[bad]
document.body.appendChild(createDivElement());
document.body.appendChild(createDivElement());
...
[good]
var frag = document.createDocumentFragment();
frag.appendChild(createDivElement());
frag.appendChild(createDivElement());
....
document.body.appendChild(frag);](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-39-320.jpg)
![Efficient JavaScript Tips
Using array join instead of directly concatenate strings.
[bad
]
]
var a = 'Hel';
a += 'lo';
a += ', wor';
a += 'ld!';
[good]
var buf = ['Hel'];
buf.push('lo');
buf.push(', wor');
buf.push('ld!');
a = buf.join('');](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-40-320.jpg)
![Efficient JavaScript Tips
Faster trim method: (use simple regular expression)
[bad]
str.replace(/^s+|s+$/g, '');
[better]
str.replace(/^s+/, '').replace(/^s+$/, '');
[much better]
str = str.replace(/^s+/, '');
for (i = str.length - 1; i >=0; i--) {
if (/S/.test(str.charAt(i))) {
str = str.substring(0, i + 1);
break;
}
}](https://image.slidesharecdn.com/tuningwebperformance-100531210602-phpapp02/85/Tuning-web-performance-41-320.jpg)
Tuning web performance
- 1. Tuning Web Performance in Frontend Perspective Lin-Chieh Shangkuan (上官林傑) ericsk@gmail.com
- 2. AGENDA The Impacts of Web Performance Development Tools Website Optimization Concepts References
- 3. The Impact of Performance Longer response time from web server. Too many requests (css/javascript files, images, flashes, ...) Complicated DOM structure Inefficient JavaScript codes ....
- 4. The Impact of Performance Longer response time from web server. Too many requests (css/javascript files, images, flashes, ...) Complicated DOM structure Inefficient JavaScript codes 80~90% time spent on the frontend
- 6. Development Tools Firefox http://getfirefox.com/ Firebug http://getfirebug.com/ Page Speed (Firebug plugin) http://code.google.com/speed/page-speed/ Y!Slow http://developer.yahoo.com/yslow/
- 7. Development Tools (cont) Chrome (Chromium/WebKit) Developer Tools http://www.chromium.org/devtools Install AMAP Latest Web Browsers e.g. IE8/9 (preview), Firefox 3.6/nightly, Safari 4/WebKit, Chrome/Chromium, Opera 10/10.5
- 8. Firebug Console Debugging your JavaScript code. Use console object in your JavaScript code. Interactive in the console tab.
- 9. Requests Analysis Analyzing the requests.
- 10. Listen to Suggestions Follow the suggestions from PageSpeed (or Y!Slow)
- 12. HTTP Overviews Request: GET /foo/bar.js HTTP/1.1 Host: example.com User-Agent: Mozilla/5.0 Response: HTTP/1.1 200 OK Content-Type: application/x-javascript Last-Modified: Mon, 15 Mar 2010 10:00:00 GMT Content-Length: 1234 (function(){ .....
- 13. HTTP Reuqest Example $ telnet ajax.googleapis.com 80 Trying 74.125.153.95... Connected to googleapis-ajax.l.google.com. Escape character is '^]'. GET /ajax/libs/jquery/1.4.2/jquery.min.js HTTP/1.1 Host: ajax.googleapis.com User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; zh-TW; rv:1.9.2) Gecko/20100115 Firefox/3.6 GTB7.0 Accept-Encoding: gzip,deflate HTTP/1.1 200 OK Content-Type: text/javascript; charset=UTF-8 Last-Modified: Mon, 15 Feb 2010 23:30:12 GMT Date: Mon, 15 Mar 2010 08:39:18 GMT Expires: Tue, 15 Mar 2011 08:39:18 GMT Vary: Accept-Encoding X-Content-Type-Options: nosniff Server: sffe Content-Encoding: gzip Cache-Control: public, max-age=31536000 Age: 2497 Content-Length: 24678 X-XSS-Protection: 0 ;iw?F???+??m?@ə???v?I։/M???6???????$e???...
- 14. Ways to Speed up the Website Optimize the backend processing e.g., PHP engine, database, .... Scaling Transfers Co-location, CDN, ... Reducing the browser's requests CSS sprites, expire headers, http compression... Optimizing the contents Defer loading, rearrangement, ... Efficient JavaScript development Improving the programming techs, ...
- 15. Scaling Transfers Use CDN e.g., Akamai, Amazon S3, ... Pixnet experience: http://www.slideshare.net/gslin/using-cdn- to-improve-performance Reduce DNS Lookups Keep-Alive fewer domains Avoid Redirects Use Comet
- 16. Scaling Transfers Sharding Dominant Domains browser HTTP/1.1 HTTP/1.0 IE6, 7 2 4 IE8 6 6 FF2 2 8 FF3 6 6 Saf 4 4 Chrome 6 6 Op 4 4 Connections per server
- 18. HTTP Compression Modern browsers support HTTP compression -- to reduce the size of response content Gzip the static (html, css, js, ...) files Don't compress everything (e.g., jpg, png, pdf, ... they are already compressed) Check if the Accept-Encoding header has gzip or deflate value. Respond Content-Encoding: gzip header.
- 19. HTTP Compression In Apache httpd server, use mod_gzip (httpd 1.3) or mod_deflate (httpd 2.x). [mod_deflate] AddOutputFilterByType DEFLATE text/html text/css application/x-javascript Problems: Proxy may cache uncompressed content Add Vary: Accept-Encoding header IE6 bug: Q312496, Q313712
- 20. Make Fewer Requests CSS Sprites: Combine N icons into 1 bigger image. Reduce N requests info 1 request. Be careful of the arrangement of the icons sample: http://www.google.com.tw/images/nav_logo8.png tool: http://tw.spritegen.website-performance.org/ http://csssprites.com/ Combine CSS/JavaScript files Using Google Closure Compiler Apache: http://code.google.com/p/modconcat/ Lighttpd: http://code.google.com/p/lighttpd-mod-concat/ YUI Comobo Handler: http://yuiblog. com/blog/2008/07/16/combohandler/
- 21. Make Fewer Requests Reduce Cookie size (or split domains) Inline images: using base64 encoding <img src="data:image/png;base64, xxxxx"> IE7/6 doesn't support this feature Useful in mobile browser Not only images: <frame src="data:text/html,%3Chtml%3E% 3Cbody%20style%3D%22background..."></frame>
- 22. Using Expires Headers Use Expires header to tell the browser how long to keep the resource. Browser won't fetch the resource again until the expire time Apache mod_expires module can help setting expire time <FilesMatch ".(css|js|jpg|png)$"> ExpiresDefault "access plus 1 year" </FilesMatch> e.g., Expires: Fri, 25 Mar 2011 08:00:00 GMT Cache-Control header In stead of using a specified date, Cache-Control header shows HOW LONG the client should keep it e.g., Cache-Control: max-age=31536000 # cache 1 year
- 23. Using Last-Modified Headers Use Last-Modified header to tell the browser the last modified time of the resource. [request] [request] GET /foo/bar.css HTTP/1.1 GET /foo/bar.css HTTP/1.1 .... ... If-Modified-Since: Thu, 25 Mar 2010 [response] 10:00:00 GMT HTTP/1.1 200 OK ... Content-Type: text/css Last-Modified: Thu, 25 Mar 2010 10: [response] 00:00 GMT+8 HTTP/1.1 304 Not Modified .... ... (empty response body)
- 24. Configuring ETag ETag (Entity Tag) header tells browser which to cache How ETag works: read Wikipedia Problem: Not-the-same tag across different servers Apache: inode-size-timestamp IIS: timestamp:changenumber Solution: Set ETag manually Remove it. (in Apache) FileETag none
- 25. Invalidates the Cached Resources If the static resources are cached, how to invalidate them? Use signature in filename ( /js/foo.AB32FDC.js ) Add query string ( /js/foo.js?20100325110000 )
- 27. Minifying JavaScript Reduce the size of JavaScript files. Reduce the total response sizes. HTML, CSS files can be also compressed. Closure-compiler Web-based http://closure-compiler.appspot.com/ RESTful API http://code.google.com/closure/compiler/docs/api-ref.html Standalone executable Ofuscation Reduce the length of variables names Be careful the obfuscation method (e.g., eval cause performance degradation) Be careful the conflicts.
- 28. Optimizing Images Using appropriate image format and remove redundant chunks in the image files. PNG8 (256 colors) is a good choice. Optimizing: Crushing PNGs pngcrush (http://pmt.sf.net/pngcrush/) Stripping JPEG metadata jpegtran (http://jpegclub.org/) Convert GIF to PNG ImageMagick Optimizing GIF animations gifsicle ( (http://www.lcdf.org/gifsicle/) Avoid image scaling
- 29. Put Stylesheets on The Top Browser delays showing any visible components while it and user wait for the stylesheet at the bottom. Use <link> to include stylesheets @import MUST precede all other rules @import may cause blank white screen phenomenon (in IE)
- 30. Put JavaScripts at The Bottom JavaScript blocks parallel downloads Put at top: the other components are delayed- loaded. defer attributes: Firefox still blocks other downloads
- 31. Non-blocking Loading Scripts IE8 is the first browser that supports downloading scripts in parallel. Ways to load JavaScripts XHR Eval XHR Inject Script in iframe Inserting script DOM element document.write
- 32. Non-blocking Loading Scripts Existing Busy Preserve Tech Parallel Diff Domain Scripts indicator Order Normal IE8, SF4 Y Y IE, SF4 IE, SF4 XHR Eval * N N SF, Ch XHR Injection * N Y SF, Ch Script in iframe * N N IE, FF, SF, Ch Script DOM * Y Y FF, SF, Ch FF, Op IE, SF4, Ch2, Script Defer Y Y * * FF3.1 IE, SF4, Ch2, document.write Y Y * * Op
- 33. iframes iframes are heavy and block onload event. Use script DOM injection to insert ADs instead of iframes.
- 35. Make JavaScript/CSS External Reusing components Cache the files Unobstrusive JavaScripts
- 36. Simplifying CSS Selectors CSS selector policy: Rightmost-First Tips: Avoid * selector Don't qualify ID/CSS selectors Specific rules Avoid descendant selectors Avoid Tag > Child selectors Rely on inheritance
- 37. Efficient JavaScript Tips Using className instead of modifying style attributes of a DOM element. [bad ] var foo = document.getElementById('foo'); foo.style.color = '#f00'; foo.style.fontWeight = 'bold'; [good] .highlight { color: #f00; font-weight: bold; } foo.className = 'highlight';
- 38. Efficient JavaScript Tips (con'd) Appending a newly-created DOM element after modifying its attributes. (avoid reflows) [bad] var foo = document.createElement('div'); document.body.appendChild(foo); foo.innerHTML = 'Hello, world'; foo.className = 'hello'; [good] var foo = document.createElement('div'); foo.innerHTML = 'Hello, world'; foo.className = 'hello'; document.body.appendChild(foo);
- 39. Efficient JavaScript Tips Using document fragment to create new contents. [bad] document.body.appendChild(createDivElement()); document.body.appendChild(createDivElement()); ... [good] var frag = document.createDocumentFragment(); frag.appendChild(createDivElement()); frag.appendChild(createDivElement()); .... document.body.appendChild(frag);
- 40. Efficient JavaScript Tips Using array join instead of directly concatenate strings. [bad ] ] var a = 'Hel'; a += 'lo'; a += ', wor'; a += 'ld!'; [good] var buf = ['Hel']; buf.push('lo'); buf.push(', wor'); buf.push('ld!'); a = buf.join('');
- 41. Efficient JavaScript Tips Faster trim method: (use simple regular expression) [bad] str.replace(/^s+|s+$/g, ''); [better] str.replace(/^s+/, '').replace(/^s+$/, ''); [much better] str = str.replace(/^s+/, ''); for (i = str.length - 1; i >=0; i--) { if (/S/.test(str.charAt(i))) { str = str.substring(0, i + 1); break; } }
- 42. Efficient JavaScript Tips Use popular JavaScript frameworks. (e.g. jQuery)
- 43. Misc.
- 44. Responsive Web Applications Prefetching resources AJAX Avoid long-running scripts
- 45. HTML5 http://whatwg.org/html5 Short tags: <!DOCTYPE html> <meta charset="UTF-8"> <script src="xxx.js">, <style>...</style> <script async ...> Application Cache (offline data) https://developer.mozilla.org/En/Offline_resources_in_Firefox http://www.whatwg.org/specs/web-apps/current- work/multipage/offline.html http://googlecode.blogspot.com/2009/04/gmail-for-mobile- html5-series-using.html WebStorage/WebDatabase API
- 46. Mobile Web Mobile device has lower hardware-profile so that the web performance is more important! iPhone Safari/Android browser/Opera Mini likes HTML5 (w/ a little CSS3)
- 47. References
- 48. Books High Performance Web Sites, O'Reilly Even Faster Web Sites
- 49. Websites Let's Make the Web Faster (Google) http://code.google.com/speed Exceptional Performance (Yahoo!) http://developer.yahoo.com/performance/ High Performance Web Sites Blog http://www.stevesouders.com/blog/