Benchmark: ClassList add vs className +=

HTML Preparation code:

<div id="one" class="firstClass secondClass"></div>

Script Preparation code:

var elem = document.getElementById("one");

Tests:

Rendered benchmark preparation results:

Previous results

Test case name	Result
classList
className

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Latest run results:

Run details: (Test run date: 3 years ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:86.0) Gecko/20100101 Firefox/86.0

Browser/OS: Firefox 86 on Windows

Test name	Executions per second
classList	2103859.0 Ops/sec
className	1660.4 Ops/sec

ClassList add vs className += (version: 0)