Run results for: document.querySelector vs document.body.querySelector vs getElementsByClassName

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4430.212 Safari/537.36

Browser: Chrome 90

Operating system: Mac OS X 10.14.6

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
querySelector	2850874.0 Ops/sec
querySelector.body	3026840.5 Ops/sec
getElementsByClassName	3683085.2 Ops/sec
getElementsByClassName BODY	3361874.2 Ops/sec

HTML Preparation code:

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

Tests:

querySelector
var el = document.querySelector('.testElement');
querySelector.body
var el = document.body.querySelector('.testElement');
getElementsByClassName
var el = document.getElementsByClassName('testElement');
getElementsByClassName BODY
var el = document.body.getElementsByClassName('testElement');