Run results for: getElementsByClassName VS querySelectorAll (simple comparison)

Run details:

User agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0

Browser: Firefox 88

Operating system: Ubuntu

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
The method getElementsByClassName()	4201428.0 Ops/sec
The method querySelectorAll()	567763.9 Ops/sec

HTML Preparation code:

<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>
<div class="example container"></div>

Tests:

The method getElementsByClassName()
document.getElementById("example container");
The method querySelectorAll()
document.querySelectorAll(".example.container");

Run results for: getElementsByClassName VS querySelectorAll (simple comparison)

A simple comparison of performance between these two methods. (Medium, @benlmsc)

The method getElementsByClassName()

The method querySelectorAll()