The contains() method of the DOMTokenList interface returns a boolean value — true if the underlying list contains the given token, otherwise false.

token

A string representing the token you want to check for the existence of in the list.

A boolean value, which is true if the calling list contains token, otherwise false.

In the following example we retrieve the list of classes set on a <span> element as a DOMTokenList using Element.classList. We then test for the existence of "c" in the list, and write the result into the <span>'s Node.textContent.

First, the HTML:

<span class="a b c"></span>

Now the JavaScript:

const span = document.querySelector("span");
span.textContent = span.classList.contains("c")
  ? "The classList contains 'c'"
  : "The classList does not contain 'c'";

The output looks like this: