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Shifting Gears
 

Shifting Gears

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My first talk at geekmeet Sweden, talking about basics of web site performance.

My first talk at geekmeet Sweden, talking about basics of web site performance.

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    Shifting Gears Shifting Gears Presentation Transcript

    • Shifting your site into the next gear http://www.flickr.com/photos/fabiovenni/91780334/ Christian Heilmann | http://wait-till-i.com | http://twitter.com/codepo8 GeekMeet, Stockholm, Sweden, December 2008
    • Hello there...
    • I’m Chris.
    • It is great to be in Sweden...
    • ...especially when you live in England...
    • Ok, I originally meant not to make any naughty jokes.
    • But then I saw the Adwords Robert seems to have bought for GeekMeet.
    • ... enough of this, let’s get serious ...
    • The performance of your web product is immensely important
    • And there are several small tricks and ideas that can increase the performance significantly.
    • There is a lot of research being done on the subject in a lot of companies...
    • ...and this information is available for free for you.
    • I’ll provide the links and names later...
    • ...but for now let’s see what is slowing our sites down.
    • http://www.flickr.com/photos/pikerslanefarm/2428232674/ Things that slow you down
    • <script>
    • JavaScript is awesome.
    • Browsers think so, too.
    • Which means that every time they encounter a script node they take a break. <script> </script>
    • Rendering stops and the JavaScript parser takes over.
    • If there is code inside the tag, this code is analyzed and executed before the browser goes back to rendering.
    • If there is a src attribute, the file it points to gets loaded, parsed and executed.
    • This can take time as the browser (with third party files) needs to get the right domain information, contact the other server, get the file and then move on.
    • This gets worse the more script nodes you use.
    • The first question is then where to put scripts?
    • The gospel according to Heilmann, 2006:
    • <!DOCTYPE HTML PUBLIC quot;-//W3C//DTD HTML 4.01//ENquot; quot;http://www.w3.org/TR/html4/strict.dtdquot;> <html lang=quot;se-se(bork bork)quot;> <head> <meta http-equiv=quot;Content-Typequot; content=quot;text/ html; charset=utf-8quot; /> <title></title> <script type=quot;text/javascriptquot; src=quot;myscripts.jsquot;></script> </head> <body> <!-- lots of HTML here --> </body> </html>
    • This has some benefits:
    • You can be sure your JavaScript is loaded before the document is displayed.
    • You make it easier for other developers to debug – they know where the scripts are.
    • On the other hand...
    • You delay the display of the page until all the scripts are loaded and executed.
    • You need to delay the access to any HTML to change or enhance until it is available – onload, onavailable, oncontentloaded.
    • This is hacky!
    • The gospel according to performance specialists 2007/2008:
    • <!DOCTYPE HTML PUBLIC quot;-//W3C//DTD HTML 4.01//ENquot; quot;http://www.w3.org/TR/html4/strict.dtdquot;> <html lang=quot;se-se(bork bork)quot;> <head> <meta http-equiv=quot;Content-Typequot; content=quot;text/ html; charset=utf-8quot; /> <title></title> </head> <body> <!-- lots of HTML here --> <script type=quot;text/javascriptquot; src=quot;myscripts.jsquot;></script> </body> </html>
    • The benefits are:
    • Your scripts don’t delay the rendering of the HTML.
    • HTML is available for enhancing.
    • The problems:
    • You don’t put scripts where people normally expect them.
    • The HTML is already available for people to interact with before you can apply your enhancement voodoo.
    • The recipe for performance and usability success?
    • Of course you need testing on your apps and sites to find your perfect solution...
    • But here are some ideas:
    • How about a mix of both?
    • <!DOCTYPE HTML PUBLIC quot;-//W3C//DTD HTML 4.01//ENquot; quot;http://www.w3.org/TR/html4/strict.dtdquot;> <html lang=quot;se-se(bork bork)quot;> <head> <meta http-equiv=quot;Content-Typequot; content=quot;text/html; charset=utf-8quot; /> <title></title> <script type=quot;text/javascriptquot; src=quot;main.jsquot;></ script> </head> <body> <!-- lots of HTML here --> <script type=quot;text/javascriptquot; src=quot;secondary.jsquot;></ script> </body> </html>
    • You can even execute delayed without hacks.
    • <!DOCTYPE HTML PUBLIC quot;-//W3C//DTD HTML 4.01//ENquot; quot;http://www.w3.org/TR/html4/strict.dtdquot;> <html lang=quot;se-se(bork bork)quot;> <head> <meta http-equiv=quot;Content-Typequot; content=quot;text/html; charset=utf-8quot; /> <title></title> <script type=quot;text/javascriptquot; src=quot;main.jsquot;></ script> </head> <body> <!-- lots of HTML here --> <script type=quot;text/javascriptquot;>doStuff()</script> <script type=quot;text/javascriptquot; src=quot;secondary.jsquot;></ script> </body> </html>
    • The first script can set a class called js on the body of the document.
    • Which allows you to define two styles, one for the non- scripting version and one for the dynamic one.
    • In the dynamic one you hide the problematic elements that could be activated prematurely.
    • Once the functionality has been added, add another class that undoes this.
    • .js #buttons{ position:absolute; top:0; left:-6000px; } .jsloaded #buttons{ position:relative; top:0; left:0; }
    • CSS parsers are very fast!
    • What about the multiple scripts issue?
    • Chunking your JavaScript into several includes all doing one job at a time is a great idea to keep your solutions maintainable.
    • <script type=quot;text/javascriptquot; src=quot;config.jsquot;> </script> <script type=quot;text/javascriptquot; src=quot;base.jsquot;> </script> <script type=quot;text/javascriptquot; src=quot;effects.jsquot;> </script> <script type=quot;text/javascriptquot; src=quot;validation.jsquot;> </script> <script type=quot;text/javascriptquot; src=quot;widgets.jsquot;> </script>
    • This does not mean though that you need to add all of them as single includes.
    • You can easily write a backend script that does that for you:
    • <script type=quot;text/javascriptquot; src=quot;/pack/config/base/ effects/validation/widgetsquot;> </script>
    • Fun things to do in this script:
    • Run through JSLint.
    • Minify.
    • Replace all strings with an array lookup to stop IE from creating a string object for each string.
    • Instead of doing this every time the page is loaded, you can make it part of a build process.
    • And don’t forget to cache the result!
    • Get a script that does most of that from Ed Eliot: http://www.ejeliot.com/blog/73
    • The other option is to be lazy.
    • Lazy loading is a concept to load dependencies only when and if they are needed.
    • Your base.js could test for all the things that should work...
    • ...and if they do, create script nodes dynamically to load the other, chunkier parts.
    • This is a pretty nice idea as it only loads things when they are needed...
    • ...thus saving server traffic and diminishing loading time.
    • However, there are problems.
    • Asynchronous loading means you never know in which order the loaded components come back to you...
    • You can work around that by creating callbacks, as explained on 24ways last year: http://24ways.org/2007/keeping-javascript- dependencies-at-bay
    • There are a lot more issues, for example that you might block document.write() of bad code ads in your page.
    • Steve Souders and Stoyan Stefanof have the whole scoop: http://stevesouders.com/tests/ delayed-script-execution.php http://yuiblog.com/blog/2008/07/22/ non-blocking-scripts/
    • What other things slow you down?
    • <img>
    • Images are what made the web what it is now.
    • Sure, linking text was a revolution.
    • But being able to get images on demand and store them was something that triggered the “collector” in everyone.
    • Yeah, Pr0n.
    • Anyways, too many images slow down your site immensely.
    • The reasons are the same delays you experience with external scripts...
    • ...except images don’t stop the rendering.
    • However only a few get loaded at a time...
    • ...as the number of parallel connections of browsers is limited (with good reason)
    • Which means you should cut down on the amount of images.
    • The best trick there is to use CSS sprites.
    • And again, Ed Eliot and Stuart Colville come to the rescue! http://spritegen.website- performance.org/
    • You use Spritegen by uploading a zip of images...
    • ...and it generates the CSS and the sprite image for you!
    • It is also open source in case you want to host it yourself.
    • How good are you in optimizing images?
    • Probably not as good as you think you are.
    • A lot of bytes can be squeezed out of images...
    • ...without changing their visual outcome.
    • Choosing the right format in the right version can be quite a drag.
    • And it doesn’t help that tools put all kind of pointless data into images (edited with xyz, version abc...).
    • The easy way out?
    • http://smushit.com
    • What else could be a problem?
    • How about the amount of images on the page?
    • You can work around loading all the images by – once again – delaying the loading.
    • The easy way is to prepend the images with a dummy and then replace this.
    • <img src=”dummy.gif#kitten.jpg” alt=”a nice kitten”> <img src=”dummy.gif#puppy.jpg” alt=”a nice puppy”> <script type=quot;text/javascriptquot;> window.onload = function(){ var imgs = document.getElementsByTagName(‘img’); for(var i=0;imgs[i];i++){ var src = imgs[i].src; imgs[i].src = src.replace(‘dummy.gif#’,’’); } } </script>
    • The more complex but cleverer way is to wait until the images are in the viewport. http://developer.yahoo.com/yui/imageloader/
    • You can see this trick in action at shine.yahoo.com and YouTube.
    • It’d be cool if browsers did that anyways – anyone remember lowsrc?
    • What else is slowing us down?
    • <object>, err <embed> err...
    • Flash and other plugins have the same issues as <script> has.
    • You interfere with the browsers’ normal rendering and they wait until the confusion is over.
    • The other issue of course is that making embedding work and validate is a pain.
    • The solution for this is progressively enhancing Flash embedding.
    • http://swfobject.googlecode.com
    • As you embed with JavaScript you can test for the correct Flash support.
    • And you can delay the embedding by for example enhancing an image when the user clicks on it.
    • SUMMARY TIME!
    • In general there are two things to do:
    • Collate and Delay :)
    • The tips and tools: ★ http://developer.yahoo.com/performance/ ★ http://www.stevesouders.com/ ★ http://website-performance.org/ ★ YSlow: http://developer.yahoo.com/yslow/ ★ Hammerhead: http://stevesouders.com/hammerhead/
    • THANSK! Svenska? Christian Heilmann http://scriptingenabled.org | http://wait-till-i.com twitter/flickr: codepo8