Run results for: querySelector() vs getElementsByTagName()[0] prerun

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:139.0) Gecko/20100101 Firefox/139.0

Browser: Firefox 139

Operating system: Mac OS X 10.15

Device Platform: Desktop

Date tested: one year ago

getElementsByTagName()[0]

48.9M/s

querySelector

27.8M/s

View exact numbers

Test name	Executions per second
✓ getElementsByTagName()[0]	48,881,716 Ops/sec
querySelector	27,767,724 Ops/sec

HTML Preparation code:

<div>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
  <span></span>
</div>

Script Preparation code:

const div = document.getElementsByTagName('div')[0];
const list = div.getElementsByTagName('span');

Tests:

querySelector
const span = div.querySelector('span');
getElementsByTagName()[0]
const span = list[0]