Run results for: getElementById + getElementByClassName vs querySelector

Run details:

User agent: Mozilla/5.0 (iPhone; CPU iPhone OS 18_4 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/18.4 Mobile/15E148 Safari/604.1

Browser: Mobile Safari 18

Operating system: iOS 18.4

Device Platform: Mobile

Date tested: one year ago

Test name	Executions per second
getElementById + getElementByClass	40607756.0 Ops/sec
querySelector	8496120.0 Ops/sec

HTML Preparation code:

<div id="testElement">
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
  <div class="testElementChild"></div>
</div>

Tests:

getElementById + getElementByClass
var el = document.getElementById('testElement'); var children = el.getElementsByClassName('testElementChild'); var length = children.length;
querySelector
var el = document.querySelector('#testElement .testElementChild'); var length = el.length;