Run results for: classList contains+add vs. add-only

Run details:

User agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:87.0) Gecko/20100101 Firefox/87.0

Browser: Firefox 87

Operating system: Ubuntu

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
contains + add	611834800.0 Ops/sec
add only	2625427.0 Ops/sec

HTML Preparation code:

<div id="foo"></div>

Script Preparation code:

var test_element = document.getElementById("foo");
if (Math.random() < 0.5) { test_element.classList.add('scrolling'); }

Tests:

contains + add
if (!test_element.classList.contains('scrolling')) { test_element.classList.add('scrolling'); }
add only
test_element.classList.add('scrolling');