Run results for: data-attribute vs className

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.90 Safari/537.36

Browser: Chrome 89

Operating system: Mac OS X 10.15.7

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
className	5745.8 Ops/sec
data-attribute	3231.4 Ops/sec

HTML Preparation code:

<div id="foo"></div>
<style>
  #foo {
    height: 50px;
    box-shadow: 0 0 0 red;
  }
  #foo.bar {
    box-shadow: 0 0 0 3px red;
  }
  #foo[data-baz] {
  }
</style>

Tests:

className
var element = document.getElementById("foo"); var i = 1000; while (i--) { element.className = "bar"; }
data-attribute
var element = document.getElementById("foo"); var boxShadow = element.style.boxShadow.split(' '); boxShadow[3] = '3px' boxShadow = boxShadow.join(' '); var i = 1000; while (i--) { element.setAttribute('baz', "1"); }