Run results for: matchMedia vs clientWidth

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:99.0) Gecko/20100101 Firefox/99.0

Browser: Firefox 99

Operating system: Mac OS X 10.15

Device Platform: Desktop

Date tested: 2 years ago

Test name	Executions per second
clientWidth	6141235.0 Ops/sec
matchMedia	1501048.0 Ops/sec
Get Background Colour from Jquery	852172.9 Ops/sec
before	195560.0 Ops/sec

HTML Preparation code:

<script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
<style>
  #before:before {
  	content: "a";
 	 display: none;
  }
  @media(min-width: 200px) {
  	#body {
  		background: red;
  	content: "b";
  	}
  }
  @media(min-width: 600px) {
  	#body {
  		background: blue;
  	content: "c";
  	}
  }
  @media(min-width: 1000px) {
  	#body {
  		background: yellow;
  	content: "d";
  	}
  }
</style>
<div id="body">
</div>

Tests:

clientWidth
document.documentElement.clientWidth;
matchMedia
window.matchMedia("(min-width: 400px)").matches;
Get Background Colour from Jquery
$("#body").css('background-color');
before
window.getComputedStyle(document.getElementById('body'), ':before').getPropertyValue('content').replace(/\"/g, '');

Run results for: matchMedia vs clientWidth

clientWidth

matchMedia

Get Background Colour from Jquery

before