DOMTokenList

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

The DOMTokenList interface represents a set of space-separated tokens. Such a set is returned by Element.classList or HTMLLinkElement.relList, and many others.

A DOMTokenList is indexed beginning with 0 as with JavaScript Array objects. DOMTokenList is always case-sensitive.

Instance properties

DOMTokenList.length Read only: An integer representing the number of objects stored in the object.
DOMTokenList.value: A stringifier property that returns the value of the list as a string.

Instance methods

DOMTokenList.item(): Returns the item in the list by its index, or null if the index is greater than or equal to the list's length.
DOMTokenList.contains(): Returns true if the list contains the given token, otherwise false.
DOMTokenList.add(): Adds the specified tokens to the list.
DOMTokenList.remove(): Removes the specified tokens from the list.
DOMTokenList.replace(): Replaces the token with another one.
DOMTokenList.supports(): Returns true if the given token is in the associated attribute's supported tokens.
DOMTokenList.toggle(): Removes the token from the list if it exists, or adds it to the list if it doesn't. Returns a boolean indicating whether the token is in the list after the operation.
DOMTokenList.entries(): Returns an iterator, allowing you to go through all key/value pairs contained in this object.
DOMTokenList.forEach(): Executes a provided callback function once for each DOMTokenList element.
DOMTokenList.keys(): Returns an iterator, allowing you to go through all keys of the key/value pairs contained in this object.
DOMTokenList.toString(): Returns the DOMTokenList.value, the space-separated values of the list as a string.
DOMTokenList.values(): Returns an iterator, allowing you to go through all values of the key/value pairs contained in this object.

In the following simple example, we retrieve the list of classes set on a <p> element as a DOMTokenList using Element.classList, add a class using DOMTokenList.add(), and then update the Node.textContent of the <p> to equal the DOMTokenList.

First, the HTML:

html

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

Now the JavaScript:

let para = document.querySelector("p");
let classes = para.classList;
para.classList.add("d");
para.textContent = `paragraph classList is "${classes}"`;

The output looks like this:

Trimming of whitespace and removal of duplicates

Methods that modify the DOMTokenList (such as DOMTokenList.add()) automatically trim any excess Whitespace and remove duplicate values from the list. For example:

html

<span class="    d   d e f"></span>

let span = document.querySelector("span");
let classes = span.classList;
span.classList.add("x");
span.textContent = `span classList is "${classes}"`;

The output looks like this: