Posts Tagged ‘jquery’

Context in live events in jQuery 1.4

January 10, 2010

Performance tests continued

In my previous post I measured how the performance of a web application is impacted by jQuery live events. The conclusion was that live events will normally not have a big performance impact, but in complex applications with lots of events it can be a problem. An important factor that I didn’t cover very well is the level of nesting in the dom-tree. I have created a test case that demonstrates better how the performance impact changes with a more nested dom-tree.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

  <head>
    <title>jQuery 1.4a2 nested live tester</title>
  </head>

  <body>
    <div id="result1">waiting for results...</div>
    <div id="result2">waiting for results...</div>
    <div id="result3">waiting for results...</div>
    <div id="result4">waiting for results...</div>
    <div id="result5">waiting for results...</div>
    <div id="result6">waiting for results...</div>
    <div id="result7">waiting for results...</div>

    <script type="text/javascript" src="jquery-1.4a2.min.js"></script>
    <script type="text/javascript">

    /*<![CDATA[*/

      jQuery(document).ready(function(){

        function measureClick(target, output, text) {
          target = jQuery(target);
          var count = 1;
          var start = new Date();
          for(var i=0; i<count; i++) {
            target.click();
          }
          var stop = new Date();
          jQuery(output).html(text + ((stop.getTime() - start.getTime())/count) + 'ms');
        }

        function addEvents(count, selector) {
          for(var i=0; i<count; i++) {
            jQuery(selector + i).live('click', function() {});
          }
        }

        //Add nested DOM-tree
        var element = jQuery('body');
        for(var i=1; i<=30; i++) {
          element = jQuery('<div id="level'+i+'">level'+i+'</div>').appendTo(element);
        }

        addEvents(100, '.garbage');

        measureClick('#level1', '#result1', 'click at level 1: ');

        measureClick('#level5', '#result2', 'click at level 5: ');

        measureClick('#level10', '#result3', 'click at level 10: ');

        measureClick('#level15', '#result4', 'click at level 15: ');

        measureClick('#level20', '#result5', 'click at level 20: ');

        measureClick('#level25', '#result6', 'click at level 25: ');

        measureClick('#level30', '#result7', 'click at level 30: ');
      });

    /*]]>*/

    </script>

  </body>

</html>

In this test we have a dom-tree with 30 nested div’s and we register 100 live events. We then trigger a click event on different levels of the tree and measure the time required to process it. On my macbook I get the following result:

click at level 1: 24ms
click at level 5: 54ms
click at level 10: 91ms
click at level 15: 130ms
click at level 20: 174ms
click at level 25: 210ms
click at level 30: 253ms

We see that the performance impact of the live events is greater on clicks that are made deep down a nested dom-tree.

Can the context help?

In my previous post on performance in jquery live events I proposed that it would be a good improvement to support a scope for the live events, so that the performance impact can be limited to a specific part in the dom-tree. One way to implement this  could be through the context parameter in the core jQuery() object constructor.  When live events were introduced they did not support the use of a context parameter, but the coming jQuery 1.4 release is supposed to support it. More details about this can be found at learningjquery.com. I was curious to se how this context was being used and if it would allow me to limit the impact of the live events to a specific part of dom-tree. To investigate this I modified the above test so that a context is provided when registering the live events. Note that in the previous test as well as this one i use the latest jQuery 1.4 alpha 2 release.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

  <head>
    <title>jQuery 1.4a2 nested live tester with context</title>
  </head>

  <body>
    <div id="level">current level...</div>
    <div id="result1">waiting for results...</div>
    <div id="result2">waiting for results...</div>
    <div id="result3">waiting for results...</div>
    <div id="result4">waiting for results...</div>
    <div id="result5">waiting for results...</div>
    <div id="result6">waiting for results...</div>
    <div id="result7">waiting for results...</div>

    <script type="text/javascript" src="jquery-1.4a2.min.js"></script>
    <script type="text/javascript">

    /*<![CDATA[*/

      jQuery(document).ready(function(){

        function measureClick(target, output, text) {
          target = jQuery(target);
          var count = 1;
          var start = new Date();
          for(var i=0; i<count; i++) {
            target.click();
          }
          var stop = new Date();
          jQuery(output).html(text + ((stop.getTime() - start.getTime())/count) + 'ms');
        }

        function addEvents(count, selector) {
          for(var i=0; i<count; i++) {
            jQuery(selector + i, jQuery('.context')).live('click', function() {});
          }
        }

        //Add nested DOM-tree
        var element = jQuery('body');
        for(var i=1; i<=30; i++) {
          element = jQuery('<div id="level'+i+'">level'+i+'</div>').appendTo(element);
        }

        var level = '20';
        jQuery('#level').html('context set at level ' + level);
        jQuery('#level' + level).addClass('context');

        addEvents(100, '.garbage');

        measureClick('#level1', '#result1', 'click at level 1: ');

        measureClick('#level5', '#result2', 'click at level 5: ');

        measureClick('#level10', '#result3', 'click at level 10: ');

        measureClick('#level15', '#result4', 'click at level 15: ');

        measureClick('#level20', '#result5', 'click at level 20: ');

        measureClick('#level25', '#result6', 'click at level 25: ');

        measureClick('#level30', '#result7', 'click at level 30: ');
      });

    /*]]>*/

    </script>

  </body>

</html>

In this test we use one of the nested divs as context. I was hoping that jQuery takes advantage of this context so that we don’t get any performance impact on events triggered above the context element, only events on elements inside the context should get the performance impact. However when I run the tests I get the following result:

context set at level 20
click at level 1: 30ms
click at level 5: 66ms
click at level 10: 113ms
click at level 15: 160ms
click at level 20: 207ms
click at level 25: 255ms
click at level 30: 305ms

We see that the resulting figures are similar to the results where no context was used. The live events even has slightly bigger performance impact now. Events on all elements in the dom-tree gets the performance impact regardless of which context we specify. So the context did not help us here. This is probably due to that jQuery attaches the delegating event on the document instead of the context element. We can verify that jQuery puts the events on the document element with a simple check in firebug. By opening firebug, reloading the test, and then invoking the following command in the console

 jQuery(document).data('events').live

We see that the live events are stored on the document and not on the context element. In my view it would be bad if this behavior is kept in the final release of jQuery 1.4 unless the context is still unsupported like in 1.3. Once the functionality is released it can not be changed without breaking some applications that rely on the current behavior. I guess the idea could be that live events should be kept even if you remove the context element and that you should be able to load the context element dynamically. But I think that it would be more valuable to be able to limit the performance impact by putting the delegating event on the context. It would also provide an easy way to control the lifetime of live events by simply removing the context element.

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Performance of jQuery Live events

November 30, 2009

Live events is a new feature in jQuery 1.3. It could be used as an alternative to traditional event delegation techniques. It provides a convenient way to implement event delegation. The following code will bind an event handler to the document. When events bubble up jQuery will check if any ancestor of the original target has the class myButton and delegate the event accordingly.
jQuery('.myButtton').live('click', function(){ //do stuff });
This is very convenient when your markup is loaded through ajax or created on the fly by JavaScript. The jQuery documentation provides some more info on how it works.

Performance

Anytime the user clicks anywhere on the document an event will be triggered and jQuery needs to determine if it should delegate it or not.
jQuery will of course need some cpu time to do this check which could potentially result in sluggish behaviour when the user clicks on the page.

Testcases

To help me understand what performance tradeoff I make when using live events, I have set up a few test cases.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>jQuery live tester</title>
</head>
<body>
<div id="result1">waiting for results...</div>
<div id="result2">waiting for results...</div>
<div id="result3">waiting for results...</div>
<div id="result4">waiting for results...</div>
<div id="result5">waiting for results...</div>
<div id="result6">waiting for results...</div>
<div id="result7">waiting for results...</div>
<div id="button">Button</div>
<script type="text/javascript" src="jquery.js"></script>
    <script type="text/javascript">
    /*<![CDATA[*/
jQuery(document).ready(function(){
function measureClick(output, text) {
  var target = jQuery('#button');
    var count = 10;
 
  var start = new Date();
    for(var i=0; i<count; i++) {
      target.click();
    }
    var stop = new Date();
     output.html(text + ((stop.getTime() - start.getTime())/count));
  }
  function addEvents(count, selector, context) {
    context = context || document;
    for(var i=0; i<count; i++) {
      jQuery(selector + i, context).live('click', function() {});
    }
  }
  function removeEvents(count, selector) {
    for(var i=0; i<count; i++) {
      jQuery(selector + i).die('click');
    }
  }
jQuery('#button').bind('click', function() {});
measureClick(jQuery('#result1'), 'without live events: ');
addEvents(10, '.garbage');
  measureClick(jQuery('#result2'), 'with 10 live events: ');
  removeEvents(10, '.garbage');
  addEvents(100, '.garbage');
  measureClick(jQuery('#result3'), 'with 100 live events: ');
  removeEvents(100, '.garbage');
  addEvents(200, '.garbage');
  measureClick(jQuery('#result4'), 'with 200 live events: ');
//Add large DOM-tree
  for(var i=0; i<500; i++) {
    jQuery('<div class="garbage' + i+'">garbage</div>').appendTo('body');
  }
  measureClick(jQuery('#result5'), 'with 200 live events and large dom: ');
  removeEvents(200, '.garbage');
  addEvents(100, '#garbage');
  measureClick(jQuery('#result6'), 'with 100 live events with id selector: ');
  removeEvents(100, '#garbage');
  addEvents(100, '#something div.garbage td tr div div.test');
  measureClick(jQuery('#result7'), 'with 100 live events with complex selector: ');
  removeEvents(100, '#something div.garbage td tr div div.test');
 });
    /*]]>*/
    </script>
</body>
</html>

Test results

test Firefox 3.5 IE8 IE7 Chrome Safari 4
without live events 0.3 1.6 0.5 0.2 0.3
with 10 live events 4.9 9.4 15.6 2.1 3.4
with 100 live events 45 93.8 143.8 21.5 20.5
with 200 live events 94.2 201.6 306.2 36.6 40.6
with 200 live events and large dom 92.2 201.6 306.2 36.9 41.7
with 100 live events with id selector 50.4 90.6 157.8 17.2 19.7
with 100 live events with complex selector 109.1 231.3 373.4 46.9 48.4
The tests were performed using jQuery v1.3.2 on a Pentium4 2.8GHz with 2GB RAM running win xp

Explanation of tests

Basically the tests are done by registering a number of live events and one normal event. We measure the time it takes to process the normal event to see how it gets impacted by the live events. First we measured the time it takes to handle the normal event without any live events registered. This is just to have something to compare against. The result is just a fraction of a millisecond. Next we add 10 live events to see how this impacts the performance. The event now takes 4.9 milliseconds to process in FireFox 3.5. To push it a bit we add more live events. We then see that 100 live events results in ca 45 milliseconds and 200 live events results in ca 94.2 milliseconds. It seem like the performance impact is approximately linear when adding more live events. What about dom size? In the first tests the markup is very simple with a very small dom-tree. A bigger dom-tree might have some impact on the performance. To test this we simply add 500 div’s to the dom and test again. This is what test no 5 does. Surprisingly we see that the performance impact of the live events does not get worse when the dom size increases. What about different types of selectors? One might also suspect that the performance is depending on the type of selector used. In test 3 a simple class selector was used. Test 6 instead uses an id selector and test 7 uses a more complext selector. We see that there is no big performance difference between a simple id selector and a simple class selector. However when using more complex selector the performance impact seems to be worse.

Conclusion

The tests show that adding live events will have some performance impact. As long as the number of registered live events is small the impact is not significant. However if you have a complex site with many events you may run into trouble, especially if you need to support browsers with poor JavaScript performance.

What could be done to improve this?

In my view it would have been better if jQuery would let you somehow define what element you want to register the delegating event on, so that the impact is limited to a specific context. The default could still be to add it to the document. This could be done in at least two different ways. One option could be to add the delegating event to the context given in the core jQuery(expression, context) function. I dont know enough about the internals of jQuery to say how feasible this is.
Another option could be to redefine the live method as follows:
jQuery('<where_to_attach_the_event>').live( '<delegation_selector>', eventType, eventHandler);
so the current live behaviour would be achieved by
jQuery('document').live('<delegation_selector', eventType, eventHandler)

Update:

After a comment from Jonathan Sharp I added some more tests to see how a more nested dom-tree affects the performance. When adding 30 nested divs we can see that a click deep down the tee will be affected more by the live events.

var button = jQuery('<div id="button">button<div>').appendTo('body');
button.bind('click', function() {});
addEvents(100, '.garbage');
//Add nested DOM-tree
var element = jQuery('body');
for(var i=0; i<30; i++) {
    element = jQuery('<div></div>').appendTo(element);
}

measureClick(jQuery('#result1'), 'click outside of nested elements: ');
button.appendTo(element);
measureClick(jQuery('#result2'), 'click inside of nested elements: ');

In this test I add 30 nested divs to the dom-tree and I add 100 live events. In firefox the output of this test is:

click outside of nested elements: 27.2
click inside of nested elements: 251.9

This shows that when I click on an element that is a direct child of the body, the performance is ok, but when I click an element deep down the nested divs the performance impact is much worse.

This makes it even more desirable to be able to define the context when registering a live event.

Update 2 – jQuery 1.4a1

On request I have run the same tests as above on the same machine but with the new alpha release of jQuery 1.4. The results are as follows:

test Firefox 3.5 IE8 Chrome Safari 4
without live events 0.3 1.6 0.2 0.3
with 10 live events 4.5 9.4 2.1 2.7
with 100 live events 38.5 79.8 19.6 19.9
with 200 live events 73.9 162.7 40.8 39.6
with 200 live events and large dom 79.5 167.3 42.2 39.9
with 100 live events with id selector 37.7 90.7 18.9 20.1
with 100 live events with complex selector 91.2 172 31.8 45.7

The test are not very precise. Running the tests twice will not produce the exact same results. It is clear though that the performance has been improved slightly.