jQuery.fn.each vs. jQuery.fn.quickEach

JavaScript performance comparison

Revision 66 of this test case created by Andy Harman

Info

The quickEach method will pass a non-unique jQuery instance to the callback meaning that there will be no need to instantiate a fresh jQuery instance on each iteration. Most of the slow-down inherent in jQuery’s native iterator method (each) is the constant need to have access to jQuery’s methods, and so most developers see constructing multiple instances as no issue… A better approach would be quickEach.

Added bug fix to roviury's version (it was previous faster because it wasn't doing any work).

Added James Padolsey's original quickEach for comparison.

Added "addClass" to body of loops so that JS runtime can't get fancy ideas about optimising the entire body away.

Added quickerEach for comparison.

Added my previous simple while-loops that demonstrate that quickEach should really not be required.

Preparation code

<script src="//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js">
</script>
<script>
  var a = $('<div/>').append(Array(100).join('<a></a>')).find('a');

  //Original version by James Padolsey.
  jQuery.fn.origQuickEach = (function() {
    var jq = jQuery([1]);
    return function(c) {
      var i = -1,
          el, len = this.length;
      try {
        while (++i < len && (el = jq[0] = this[i]) && c.call(jq, i, el) !== false);
      } catch (e) {
        delete jq[0];
        throw e;
      }
      delete jq[0];
      return this;
    };
  }());

  //Updated version supplied by roviury.
  jQuery.fn.updatedQuickEach = (function(jq) {
    return function(c) {
      var i = -1,
          el, len = this.length;
      try {
        while (++i < len && (el = jq[0] = this[i]) && c.call(jq, i, el) !== false);
      } catch (e) {
        throw e;
      } finally {
        delete jq[0];
      }
      return this;
    };
  })(jQuery([1])); //Bug-fix: Previously this was just jQuery().
  jQuery.fn.quickerEach = (function() {
    var jq = jQuery([1]);
    return function(c) {
      var i = -1,
          el;
      try {
        while (el = jq[0] = this[++i] && c.call(jq, i, el) !== false);
      } catch (e) {
        jq[0] = 1;
        throw e;
      }
      jq[0] = 1;
      return this;
    };
  }());
</script>

Preparation code output

Test runner

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Testing in unknown unknown
Test Ops/sec
.each
 
//Added "addClass" to give real-world feel.
a.each(function() {
  $(this).addClass("wibble");
});
 pending…
Original .quickEach
 
//Implementation by James Padolsey.
//Added "addClass" to give real-world feel.
a.origQuickEach(function() {
  this.addClass("wibble"); // jQuery object
});
 pending…
Updated .quickEach
 
//Implementation by roviury (uses finally for exception handling).
//Code is tighter, but the finally bit actually slows everything down
//(especially in Firefox).
//Added "addClass" to give real-world feel.
a.updatedQuickEach(function() {
  this.addClass("wibble"); // jQuery object
});
 pending…
quickerEach
 
//Implementation by Andy Harman.
//Added "addClass" to give real-world feel.
a.quickerEach(function() {
  this.addClass("wibble"); // jQuery object
});
 pending…
while loop
 
//Could go faster if you don't recreate the jQuery object each run.
var jq = jQuery([1]), i = -1;
while (jq[0] = a[++i]) {
  //Would obviously go faster if you go directly to the DOM instead
  //of using jQuery (performance versus maintenance).
  jq.addClass("wibble");
}
 pending…
while without body
 
//While-loop without a body is much faster that while-loop-with-body
//across all browsers that I have tested.
//This seems to be reason for the performance of quickerEach - it
//indicates that an anonymous method can be faster than using a
//while-loop that has a body section.
var jq = jQuery([1]), i = -1;
while (jq[0] = a[++i] && jq.addClass("wibble"));
 pending…

Compare results of other browsers

Revisions

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1 comment

Andy Harman (revision owner) commented : ∞

SORRY - I'm an idiot!

This test case contained a major bug. The quickerEach implementation depended on the following code:

  while (el = jq[0] = this[++i] && c.call(jq, i, el !== false);

I forgot that operator precedence would cause this to be evaluated as (note the added-brackets):

  while (el = jq[0] =   (this[++i] && c.call(jq, i, el !== false)  );

So the addClass method was chewing on a boolean rather than a DOM element.

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