getElementsByClassName VS querySelectorAll

JavaScript performance comparison

Revision 203 of this test case created by Mike Senn

Preparation code

<div>
  <ul>
    <li><a href="#" name="name" class="classname">item 1</a></li>
    <li><a href="#" name="name" class="classname">item 2</a></li>
    <li><a href="#" name="name" class="classname">item 3</a></li>
    <li><a href="#" name="name" class="classname">item 4</a></li>
    <li><a href="#" name="name" class="classname">item 5</a></li>
    <li><a href="#" name="name" class="classname">item 6</a></li>
    <li><a href="#" name="name" class="classname">item 7</a></li>
    <li><a href="#" name="name" class="classname">item 8</a></li>
    <li><a href="#" name="name" class="classname">item 9</a></li>
    <li><a href="#" name="name" class="classname">item 10</a></li>
  </ul>
  <div class="closed-shadow-root"></div>
</div>
      
<script>
Benchmark.prototype.setup = function() {
  shadow = shadow || document.querySelector('.closed-shadow-root').attachShadow({mode: 'open'})
  
  var ul = document.createElement('ul');
  shadow.appendChild(ul);
  
  for (var i = 1; i <= 10; ++i) {
      var a = document.createElement('a');
      a.className = 'classname';
      a.innerText = 'item ' + i;
      ul.appendChild(a);
  }
  
  var host = shadow.host;

};

Benchmark.prototype.teardown = function() {
  ul.remove()

};
</script>

Preparation code output

<div> <ul> <li><a href="#" name="name" class="classname">item 1</a></li> <li><a href="#" name="name" class="classname">item 2</a></li> <li><a href="#" name="name" class="classname">item 3</a></li> <li><a href="#" name="name" class="classname">item 4</a></li> <li><a href="#" name="name" class="classname">item 5</a></li> <li><a href="#" name="name" class="classname">item 6</a></li> <li><a href="#" name="name" class="classname">item 7</a></li> <li><a href="#" name="name" class="classname">item 8</a></li> <li><a href="#" name="name" class="classname">item 9</a></li> <li><a href="#" name="name" class="classname">item 10</a></li> </ul> <div class="closed-shadow-root"></div> </div>

Test runner

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Testing in CCBot 2.0.0 / Other 0.0.0
Test Ops/sec
shadow getElementsByTagName
node = host.getElementsByTagName('li')[0]
pending…
shadow getElementsByClassName
node = host.getElementsByClassName('classname')[0];
pending…
getElementsByClassName
node = document.getElementsByClassName('classname')[0];
pending…
shadow querySelectorAll
node = host.querySelectorAll('.classname')[0];
pending…
getElementsByTagName
node = document.getElementsByTagName('li')[0]
pending…
querySelectorAll
node = document.querySelectorAll('.classname')[0];
pending…

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