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

Run details:

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:138.0) Gecko/20100101 Firefox/138.0

Browser: Firefox 138

Operating system: Windows

Device Platform: Desktop

Date tested: one year ago

getElementsByTagName()[0]

20.8M/s

querySelector

7.0M/s

View exact numbers

Test name	Executions per second
✓ getElementsByTagName()[0]	20,844,598 Ops/sec
querySelector	6,983,606 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]