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    Unlearning and Relearning jQuery - Client-side Performance Optimization Unlearning and Relearning jQuery - Client-side Performance Optimization Presentation Transcript

    • Unlearning and Relearning jQuery
      Client-side Performance Optimization
      Oct 14, 2010
      1
      Created for Magma Rails 2010 - www.magmarails.com
    • Purpose and Audience
      Purpose
      Understand why client-side performance optimization is important
      Better understand jQuery and how to maximize performance when using it
      Audience
      Has a very basic understanding of client-side web development
      JavaScript, HTML, CSS
      Ideally, has used some JavaScript framework before
      jQuery, Prototype, YUI, MooTools, etc.
      If you haven’t specifically used jQuery before that’s fine. The API documentation will fill in the blanks later!
      If you’ve never used a framework before that’s fine too, this will begin to make more sense later as you write your first jQuery application.
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      2
    • Why care about the performance of client-side code?
      Myth: “It doesn’t run on my servers so it’s not important to the speed of my application.”
      Fact: Users of your website judge the performance of your application based on how long it takes for them to begin using it, not how long it takes to process and render a request on your servers
      This is includes:
      Number of requests for files to the server (this is a big deal)
      Use sprites: http://css-tricks.com/css-sprites/
      Compress JavaScript and CSS files into a single file of each type when possible: http://developer.yahoo.com/yui/compressor/
      The total size of content download
      The amount of time it takes to render the page
      The amount of time it takes until the page is ready to be interacted with
      How long it takes to process each interaction with the page
      This means that perceived performance is just as important as actual performance! We’ll talk about techniques that apply to both
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      3
    • Why use a JavaScript framework?
      Deals with browser inconsistencies for you
      You have to write a lot less code
      Lots of community contribution and therefore a more stable core for your JavaScript application
      You can upgrade to a newer version later and improve your application for free
      Did I mention that you get to write less code?
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      4
    • Why jQuery and not Prototype?
      Easier to use than Prototype
      Usually results in fewer lines of code
      jQuery has a smaller footprint
      By far the most popular JavaScript framework
      About 28% of all websites on the internet use it
      The big players use it (google, twitter, amazon, etc.)
      This means more community support and more contribution to the open source code
      Oct 14, 2010
      5
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
    • Using jQuery with Ruby on Rails
      For Rails 3
      Use the Unobtrusive JavaScript library at http://github.com/rails/jquery-ujs
      In Rails 3 the JavaScript helpers no longer mix JS with your markup (this is a very good thing!) allowing us to easily swap out JS frameworks with just a single JS file
      More instructions at http://joshhuckabee.com/jquery-rails-3
      For older versions of Rails
      Use the jRails plugin from http://github.com/aaronchi/jrails
      Replaces the default helpers in Rails to output jQuery code instead of Prototype
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      6
    • What you probably already know
      You can access elements in a page using a CSS selector
      $(‘#myDiv’) instead of document.getElementById(‘myDiv’)
      In Prototype this would be $(‘myDiv’) since the $ method looks up an element based on its ID
      $(‘.someClass’) gives you an array of all elements having a particular class
      In Prototype this would be $$(‘.someClass’) since the $$ method is the one used for selecting elements via a CSS-style selector
      You can do fun things like:
      Show and hide elements on a page
      $(‘#myDiv’).show()
      $(‘#myDiv’).hide()
      Make things happen when you click on an element
      $(‘#myDiv’).click(function(){ alert(‘clicked!’) })
      …and a bunch of other stuff too
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      7
    • What you may not know
      Some selectors can be very slow
      You don’t need to use $() every time you want to select an element
      You can chain jQuery method calls
      Usually a good idea, but not always (more on this later)
      You may be writing fewer lines of code with a JS framework but it can still make your application much slower if used improperly
      This goes for all frameworks, including Prototype
      jQuery !== JavaScript
      jQuery is NOT all-powerful!
      You still need to understand how JavaScript works without it!
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      8
    • The DOM (Document Object Model)
      Think of it as a JavaScript API for accessing HTML elements and manipulating them
      Get an element with a particular ID
      document.getElementById(‘myDiv’)
      Redirect to another page
      window.location = ‘http://example.com’
      Get all elements with a particular tag name
      document.getElementsByTagName(’div’);
      All browsers support these
      You want to favor jQuery use that directly maps to a built in DOM method because they will be the fastest
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      9
      Image courtesy of John M. Kennedy T. http://en.wikipedia.org/wiki/File:JKDOM.SVG
    • The DOM (Document Object Model)
      Terminology I’ll use
      • Descendent: All elements contained within that element
      • LINK and ANCHOR are descendents of DOCUMENT
      • TEXT and RADIO are descents of FORM
      • TEXT and RADIO are also descendents of DOCUMENT
      • Ancestor: The opposite of descendent
      • FORM is an ancestor of TEXT and RADIO
      • DOCUMENT is the ancestor of FORM, TEXT, RADIO, LINK, and ANCHOR
      • Parent: The direct ancestor of an element (only one)
      • FORM is the parent of TEXT and RADIO
      • DOCUMENT is the parent of LINK and ANCHOR
      • Children: The direct descendents of an element
      • TEXT and RADIO are children of FORM
      • TEXT and RADIO are not children of DOCUMENT (they are descendents)
      • LINK and ANCHOR are children of DOCUMENT
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      10
      Note: Examples are for the image to the right, not true for all pages
      Image courtesy of John M. Kennedy T. http://en.wikipedia.org/wiki/File:JKDOM.SVG
    • Using Firebug to look at the DOM
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      11
      Firebug is a free extension for Firefox: http://getfirebug.com/Webkit browsers (like Safari and Chrome) have similar built-in functionality.
    • The difference between DOM Ready and onload
      You can’t access a DOM element until it has been fully loaded and rendered by the browser
      onload occurs after everything on the page has been loaded
      HTML
      Stylesheets
      JavaScript (including 3rd party!)
      Images
      Content of iframes
      Comes with the browser
      window.onload = myFunction;
      <body onload=“myFunction();”>
      DOM Ready occurs when the document has been processed and all DOM objects are ready for manipulation
      Doesn’t wait for assets since they aren’t part of the DOM
      jQuery and Prototype give you this functionality
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      12
    • How do I choose?
      Put application-critical JavaScript in a DOM Ready block
      When you can’t use your application without it
      Example: critical event listeners
      $(‘#myButton’).click(loadImportantForm);
      Use onload for anything non-critical
      Deferring to onload is a good idea when possible because too much code in DOM Ready can cause the rendering of your page to stall, adding additional time until the user can interact with it
      Example: initializing animations
      $(‘#myDiv’).hover(sillyFadeOver, sillyFadeOut);
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      13
    • When do I need DOM Ready / onload?
      Simple answer: when the browser loads your JavaScript before it loads the DOM elements you need
      When you define your JavaScript in external files
      Usually you include these in the header. This means that the JavaScript file is fully loaded an begins to execute before the browser begins to load the body of your document.
      Sometimes you also include JS files within the body of your document. In this case you don’t know when the file will be ready to execute. Could happen before your DOM is ready or after it.
      When you use inline JavaScript before all required elements have been loaded
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      14
    • Does that mean I don’t always need it?
      Yes, but be careful. When in doubt, use DOM Ready or onload
      This will work
      <a id=“myAnchor” href=“#”>click me if you can</a>
      <script>document.getElementById(‘myAnchor’);</script>
      This will not
      <script>document.getElementById(‘myAnchor’);</script>
      <a id=“myAnchor” href=“#”>click me if you can</a>
      This will work in some browsers but IE < 8 will have a fit
      <body> 
      <div>
         <script type="text/javascript">
      varnewElem = document.createElement(’div');
          document.body.appendChild(newElem);
         </script>
      </div>
      </body>
      (so don’t try to use element before it has been closed)
      This applies to jQuery syntax as well
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      15
    • Using DOM Ready and onload
      Onload
      function myFunction(){
      // your code
      }
      window.onload = myFunction;// replaces onload with this function, so can only have this once
      Onload (jQuery style)
      $(window).load(function(){ // can have multiple on a page
      // your code
      });
      DOM Ready
      jQuery only and can have multiple DOM Ready blocks on a page
      Longer format
      $(document).ready(function(){
      // your code
      });
      Short version
      $(function(){
      // your code
      });
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      16
    • Common mistake with DOM Ready
      Don’t define methods in a Dom Ready block, just call them
      Works
      function myFunction(){
      // your code
      }
      $(document).ready(function(){
      myFunction();
      });
      Doesn’t work
      $(document).ready(function(){
      function myFunction(){
      // your code
      }
      myFunction();
      });
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      17
    • Getting elements faster
      Always start with an ID
      $(‘#myDiv’)
      Behind the scenes, jQuery can use the native document.getElementById() which is very fast
      Fastest way to get a DOM element
      Avoid the class selector on a large DOM node
      $(‘.myClass’)
      Very slow over a large DOM node
      No native DOM call common to all browsers
      Use a tag name when possible
      $(‘div.myClass’) is much faster than $(‘.myClass’)
      Uses document.getElementsByTagName() behind the scenes
      But remember that ID is the fastest so $(‘div#myDiv’) is actually slower than $(‘#myDiv’)
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      18
    • Getting elements faster
      Optimize selectors using the ‘right to left’ model
      As of jQuery 1.3 this the method the selector engine uses
      This means the most specific (right-most) selector is found first and then its ancestors are checked starting on the left
      Make your right-most selector very efficient
      Example
      $(‘.myClassdiv.otherClass’) is actually more efficient than
      $(‘div.myClass .otherClass’)
      However, descending from an ID is still the fastest:
      $(‘#myDivdiv.otherClass’)
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      19
    • Cache your DOM lookups
      A call to $() returns a valid jQuery object, so store it for later use
      This is bad because each line does a DOM lookup
      $(‘#myDiv .myClass’).click(myFunc);
      $(‘#myDiv .myClass’).css(‘width’, ‘250px’);
      $(‘#myDiv .myClass’).css(‘color’, ‘red’);
      This is much better
      varmyStuff = $(‘#myDiv .myClass’);
      myStuff.click(myFunc);
      myStuff.css(‘width’, ‘250px’);
      myStuff.css(‘color’, ‘red’);
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      20
    • Work with the most specific DOM element possible
      $(‘#myDiv .myClass’) is much faster than $(‘.myClass’)
      Use the find() jQuery method to search for matching elements within your cached object
      varmyDiv = $(‘#myDiv’);
      myDiv.find(‘.myClass’).hide();
      myDiv.find(‘input’).click(myFun);
      A lot of times it makes sense to cache the main elements of your page up front and use them later
      content = $(‘#content’);
      sidebar = content.find(‘#sidebar’);
      article = content.find(‘#article’);
      commentWrapper = article.find(‘#comments’);
      comments = commentWrapper.find(‘div.comment’);
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      21
    • Use chaining
      Remember that a call to $() returns a valid jQuery object, which means you can chain jQuery methods
      You can shorten the previous example:
      $(‘#myDiv .myClass’).click(myFunc);
      $(‘#myDiv .myClass’).css(‘width’, ‘250px’);
      $(‘#myDiv .myClass’).css(‘color’, ‘red’);
      To the lighter-weight:
      $(‘#myDiv .myClass’).click(myFunc).css(‘width’, ‘250px’).css(‘color’, ‘red’);
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      22
    • When not to use chaining
      Be careful chaining the DOM traversal methods
      Doing so means that your application may be too dependent on the DOM structure
      Example of what not to do:
      $(‘#myDiv’).parent().parent(); // fails if you add another element surrounding this one
      Potential alternatives:
      $(‘#myDiv’).parents(‘someTag’)
      $(‘#myDiv’).parents(‘.someClass’)
      Not about performance, but about writing good code
      Yes, the DOM structure still matters in the last two examples but it isn’t so rigid that you can’t add or remove elements in between
      And yes, the last two examples may be a little slower but not so much that it’s worth writing unsafe code
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      23
    • Avoid as much DOM manipulation as possible
      Rendering changes to the DOM is very expensive, so do as few manipulations as possible
      Example of what not to do:
      <div id=“myDiv”></div>
      <script>
      for(vari=0; i < 100; i++){
      $(‘#myDiv’).append(‘<a href=“#”>link</a>’); // The browser has to re-render this and any other effected elements at each iteration of the loop
      }
      </script>
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      24
    • Avoid as much DOM manipulation as possible
      It would be much more efficient to store all elements you wish to create in a string and then insert them one time:
      <div id=“myDiv”></div>
      <script>
      myLinks = ‘’;
      for(vari=0; i < 100; i++){
      myLinks = myLinks + ‘<a href=“#”>link</a>’;
      }
      $(‘#myDiv’).append(myLinks); // this is the only DOM manipulation
      </script>
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      25
    • Avoid as much DOM manipulation as possible
      It would be even more efficient if we wrap many individual elements in a single element and then insert that in the DOM:
      <div id=“myDiv”></div>
      <script>
      myLinks = ‘<div id=“myDiv”>’;
      for(vari=0; i < 100; i++){
      myLinks = myLinks + ‘<a href=“#”>link</a>’;
      }
      myLinks = myLinks + ‘</div>’;
      $(‘#myDiv’).replaceWith(myLinks); // instead of putting a string of 100 elements in this div we are replacing a single DOM node
      </script>
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      26
    • Avoid as much DOM manipulation as possible
      Don’t like the idea of creating a string for your DOM elements?
      Since rendering is the most expensive part, use the clone() jQuery method to make a copy of the DOM object that you can manipulate without being rendered and then insert that object into the DOM when finished
      <div id=“myDiv”></div>
      <script>
      clonedDiv = $(‘#myDiv’).clone();
      for(vari=0; i < 100; i++){
      clonedDiv.append(‘<a href=“#”>link</a>’); // clonedDiv is not visible on the page so manipulating it doesn’t cause the browser to re-render
      }
      $(‘#myDiv’).replaceWith(clonedDiv); // still the only time re-rendering occurs
      </script>
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      27
    • Avoid as much DOM manipulation as possible
      You can also improve performance of DOM manipulations by using the DocumentFragment object
      DocumentFragment is a lightweight Document object you can create, manipulate and then insert into the DOM later (much like the previous example)
      More information at: http://www.devguru.com/technologies/xmldom/quickref/obj_documentFragment.html
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      28
    • Event delegation
      Events in jQuery “bubble” up to their parent DOM elements unless you tell them not to
      You can use this to your advantage by creating a single event listener on a parent object and letting that listener determine which of its children triggered the event
      This is much more efficient than creating a many listeners on individual elements
      If you’re only binding one or two event listeners then this method isn’t really necessary
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      29
    • Event delegation
      Let’s say you have a div with 100 anchor tags and you want to hide the anchor when it’s clicked
      Instead of:
      $(‘#myDiva’).bind(‘click’, function(){
      $(this).hide();
      });
      Do this:
      $(‘#myDiv’).bind(‘click’, function(e){
      if(e.target.nodeName.toLowerCase() === 'a'){
      $(e.target).hide()
      }
      });
      e is the Event object
      Notice that e.target returns the actual DOM node, not a jQuery object, so you need to pass it to $() to get jQuery functionality
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      30
    • jQuery.delegate()
      This is the same example using jQuery’s built in event delegation method (1.4.2 and above)
      $('#myDiv').delegate('a', 'click', function(e){
      $(this).hide();
      });
      Tip: for this and the last example, use e.preventDefault() to prevent the default action of the event. In this case, following the hyperlink:
      $('#myDiv').delegate('a', 'click', function(e){
      e.preventDefault();
      $(this).hide();
      });
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      31
    • Lazy-loading assets
      Load the bare minimum up front and load the rest as needed
      Initial load and rendering of the page is much faster, allowing the user to interact with the page as quickly as possible
      Works well in many cases but sometimes waiting for something to load after the user begins to interact with the page is more frustrating, so choose wisely when it’s appropriate
      An excellent choice for non-critical 3rd party tracking scripts, especially ones that are notorious slow
      Can apply to JavaScript files, images, even CSS
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      32
    • Lazy-loading assets
      Method 1: document.write()
      Can also apply this method to other types of assets such as images and CSS
      <script>
      document.write('<script src="', ’someScript.js', '" type="text/javascript"></script>');
      </script>
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      33
    • Lazy-loading assets
      Method 2: Change the src property of an existing script tag
      This example is just for JavaScript but you could do something similar for other assets
      <script id=”lazy" type="text/JavaScript"></script>
      <script>
      document.getElementById(’lazy').src = ‘someScript.js';
      </script>
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      34
    • Lazy-loading assets
      Method 3: Use AJAX
      Applies to any type of asset
      Just add an AJAX call on DOM Ready to grab what you need
      Check out the jQuery documentation on using AJAX: http://api.jquery.com/category/ajax/
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      35
    • Lazy-loading assets
      Method 4: Use the Lazy Load jQuery plugin: http://www.appelsiini.net/projects/lazyload
      When you want to lazy load images on a very long page
      Let’s you load images visible in the browser first and delay loading of images “below the fold” (below the current browser view)
      Simplest example:
      $("img").lazyload(); // causing images below the fold to be lazy loaded
      Start loading images when they are 200px below the fold:
      $("img").lazyload({ threshold : 200 });
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      36
    • Unobtrusive JavaScript
      Keep JavaScript in external files and avoid inline JavaScript (Rails 3 does it!)
      Less code for the browser to load and interpret while rendering
      JavaScript in external files can be cached by the browser. Inline JavaScript can’t be cached
      Avoid:
      <a href=“#” onclick=“myFunc();”>run myFunc</a>
      In favor of:
      <a href=“#” id=“myLink”>run myFunc</a>
      $(‘#myLink’).bind(‘click’, myFunc); // in external file on DOM Ready
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      37
    • Unobtrusive JavaScript
      Rails 3 is a great inspiration for more advanced uses
      Uses custom attributes to indentify what events to bind on elements
      Rails helper code:
      <%= link_to "delete", domain_path(@domain), :method => :delete, :confirm => "Are you sure?" %>
      In Rails 2 this outputs a real mess:
      <a href="/domains/1" class="destroy" onclick="if (confirm('Are you sure?')) { varf = document.createElement('form'); f.style.display = 'none'; this.parentNode.appendChild(f); f.method = 'POST'; f.action = this.href;varm = document.createElement('input'); m.setAttribute('type', 'hidden'); m.setAttribute('name', '_method'); m.setAttribute('value', 'delete'); f.appendChild(m);vars = document.createElement('input'); s.setAttribute('type', 'hidden'); s.setAttribute('name', 'authenticity_token'); s.setAttribute('value', 'pKvg9hsnQ33uk='); f.appendChild(s);f.submit(); };return false;">delete</a>
      In Rails 3 the markup just looks like this:
      <a href="/domains/1" data-confirm="Are you sure?" data-method="delete" rel="nofollow">delete</a>
      An external JavaScript file (remember jquery-ujs?) uses the attributes and binds the appropriate JavaScript to the element
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      38
      Examples from http://www.simonecarletti.com/blog/2010/06/unobtrusive-javascript-in-rails-3/
    • Storing data on DOM objects
      Sometimes you need to store extra information about an element to improve efficiency, keep yourself from having to pass a bunch of variables through method calls, etc.
      It’s tempting to do one of the following:
      $(‘#myElement’).attr(‘rel’, ‘some data’); // improper use of attribute
      var data = $(‘#myElement’).attr(‘rel’);
      $(‘#hiddenInput’).val(‘some data’); // unnecessary form data
      var data = $(‘#hiddenInput’).val();
      jQuery gives you a much nicer alternative:
      $(‘#myElement’).data(‘key’, ‘value’);
      var data = $(‘#myElement’).data(‘key’);
      Note: you can also store data on a DOM object directly using standard object syntax since a DOM object is the same as any other object. Just don’t store it on a jQuery object unless you use data()
      varelem = $(‘#myElement’).get(0);
      elem.foo = ‘bar’;
      alert(elem.foo);
      But data() is safer so you generally just want to use that
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      39
    • Use for instead of each()
      The native for loop is much faster than jQuery’s each() iterator so use it when possible for large arrays
      Instead of:
      $.each (array, function (i) {
      // do something with array[i]
      });
      The same can be done with a native for loop:
      for (vari=0;i<array.length; i++) {
      // do something with array[i]
      }
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      40
    • Use short variable names and create aliases
      Reduces overall size of file, especially if not minified
      Only useful when these items are used frequently in a large JS application
      Does reduce code readability so good minification may be a better option in many cases, but some of these may not be minified so watch out
      varw = window,
      l = w.location,
      d = document,
      t = true,
      f = false,
      n = null,
      M = Math,
      o = "object",
      a = "array",
      s = "string”,
      u = "undefined";
      l = ‘http://jonathandean.com’; // redirect to another page
      if(myVar == f || myVar == n) // test if myVar is false or null
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      41
    • Other client-side performance tips
      Make the fewest number of requests to the server as possible
      Each request adds overhead and additional time to load
      Combine multiple small images into a single sprite
      Combine JS and CSS into a single file of each type when possible
      Don’t load a file you don’t need
      Compress JS and CSS to remove whitespace characters and shorten long variable and method names
      You don’t necessarily want to create “packed” files
      These files will have the smallest total size
      However, the browser needs to read in the entire file and parse it before it can be used. The parsing step is not cached and adds overhead to each page load. Often the benefit does not outweigh the cost
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      42
    • Download for later
      You can find these slides sometime tomorrow at http://www.jonathandean.com/2010/10/unlearning-and-relearning-jquery-client-side-performance-optimization/
      The short URL is http://tinyurl.com/jquery-magma
      Check http://jonathandean.com soon for an HTML version of the presentation (after a few more caguamas and a long flight home!)
      Oct 14, 2010
      Unlearning and Relearning jQuery (Client-side performance Optimization) by Jonathan Dean - www.jonathandean.com
      43