Awesome jQuery performance tips by Addy Osmani.

July 19, 2011

I'm always on the look out for ways to improve my front end development skills. I usually have to sift through heavily opinionated articles to find anything useful. Addy Osmani recently posted up a slide show with some really great performance tips. He has a bunch of great articles and I've learned a lot from them. You can check out the slides here. I'd highly highly encourage you to go through all the slides a couple times. Here are a couple of things that I took away that I now use all the time.

  1. Always use the latest version of jQuery
* Newer versions of jQuery have significant performance improvements.

* I've usually only thought to upgrade to get new features.
  1. Use ID and tag selectors whenever you can.
* getElementById and getElementByTagName are native javascript. The further you get away from native javascript, the slower it will perform. 

* I steered away from using IDs and only used class selectors for a long time. I plan on fixing that.
  1. Understand parent and children selectors.
* I use to use $('.blah', '.wrapper') all the time.  I now know that this is a much better option:  

[code lang="js"] var list = document.getElementById('list'); var $test = $(list).find('.test'); [/code] Here is where you can check out the performance of this.

  1. Use raw javascript
* Ever do this?

[code lang="js"] $('a').click(function(){ var url = $(this).attr('href'); }); [/code] This is much faster [code lang="js"] $('a').click(function(){ var url = this.href; }); [/code]


Check out a performance test here to see that using raw javascript is significantly faster that using jQuery for attributes.

  1. Event delegation
* Another item where I've done what's easier to code than what is better for performance.

[code lang="js"] $('#nav a').live('click', function(e) { e.preventDefault(); }); [/code] is slower than [code lang="js"] $('#nav').delegate('a', 'click', function(e) { e.preventDefault(); }); [/code] They both do the same thing.

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