The read-only media property of the CSSMediaRule interface MediaList represents the intended destination medium for style information.

a MediaList

The CSS includes a media query with one style rule. This will be the first CSSRule returned by document.styleSheets[0].cssRules. Calling myRules[0].media therefore returns a MediaList object representing the media query.

@media (min-width: 500px) {
  body {
    color: blue;
  }
}

let myRules = document.styleSheets[0].cssRules;
console.log(myRules[0].media); // a MediaList