<div id="test">Testing</div>
var el = document.getElementById('test');
el.setAttribute('mytest', 'true')
el.classList.add('mytest')
FAQ: FAQ
Source code: GitHub/MeasureThat.net
Report issues: MeasureThat.net/Issues
Based on: Benchmark.js
Facebook page: https://www.facebook.com/MeasureThat.Net
Python benchmarks support: Pyodide