How to Change Element's Class with JavaScript - ClassName and ClassList

How to Change Element's Class with JavaScript - ClassName and ClassList

How to Change Element's Class with JavaScript - className and classList. In this tutorial, we'll take a look at how to change an element's class in JavaScript using className and classList for modern browsers, with practical examples.

Introduction

The class attribute in HTML is used to define a class for one or more HTML elements. This way, a lot of elements can belong to the same class of elements and share the same style in the style sheet, so you don't have to write the same style for every element over and over again.

That being said, sometimes you want to change styles dynamically, depending on the user's input. For example, you want to implement day/night mode for your web page, which can effectively be done with changing element's class.

This is a common task for when you want to let the user customize any aspect of your application. In this guide - we'll take a look at how to change the class of an HTML element in JavaScript.

DOM Tree

The DOM or Document Object Model is an interface that creates a tree structure from XML or HTML. The hierarchy of the document's elements is represented through the DOM. A tree is made up of nodes and branches, where elements are nodes and elements' relations are branches. In the DOM Tree, the root node is html - the very first element necessary to start marking up an HTML document:

<!DOCTYPE HTML>
<html>
<head>
    <title>Web page title</title>
</head>
<body>
    <h1>Some heading</h1>
</body>
</html>

Note: Internet Explorer 8 and 9 do not support classList.

classList has a couple of methods that we can leverage:

  • add(class_name) - adds a new class class_name to the list.
  • remove(class_name) - removes a class class_name from the list.
  • toggle(class_name) - adds class class_name if it is not already added, otherwise removes it.
  • contains(class_name) - checks whether class_name is in the list of classes applied to the HTML element.

javascript

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