NodeList vs. array iteration

JavaScript performance comparison

Test case created by John-David Dalton

Preparation code

<div>
  <ul>
    <li><a href="#">item 1</a></li>
    <li><a href="#">item 2</a></li>
    <li><a href="#">item 3</a></li>
  </ul>
</div>
<script>
  function toArray(collection) {
   var result = [],
       i = -1;
   while (result[++i] = collection[i]) {};
   result.length--;
   return result;
  }
 
  var liveList = document.getElementsByTagName('a');
  var statList = document.querySelectorAll('a');
  var liveArr = toArray(liveList);
  var statArr = toArray(statList);
</script>

Preparation code output

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Testing in unknown unknown
Test Ops/sec
Live List
for (var i = 0, length = liveList.length; i < length; i++) {
 liveList[i].nodeName;
}
pending…
Static List
for (var i = 0, length = statList.length; i < length; i++) {
 statList[i].nodeName;
}
pending…
Array of Live List
for (var i = 0, length = liveArr.length; i < length; i++) {
 liveArr[i].nodeName;
}
pending…
Array of Static List
for (var i = 0, length = statArr.length; i < length; i++) {
 statArr[i].nodeName;
}
pending…

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