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How to Add a Class to a Given Element in JavaScript

Topic: JavaScript / jQueryPrev|Next

Answer: Use the className Property

If you want to add a class to an HTML element without replacing its existing class, you can do something as shown in the following example:

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Add Class to an Element Using JavaScript</title>
<style>
    .content{
        padding: 20px;
        border: 2px solid #ccc;
    }
    .highlight{
        background: yellow;
    }
</style>
</head>
<body>
    <div class="content" id="myDiv">
        <p>This is a paragraph of text.</p>
        <button type="button" onclick="addNewClass();">Add Class</button>
    </div>
    
    <script>
    function addNewClass(){
        // Select div element by its id attribute
        var elem = document.getElementById("myDiv");
        elem.className += " highlight";
    }
    </script>
</body>
</html>

In the example above, the addNewClass() function adds a new class highlight to the DIV element that already has a class box without removing or replacing it using the className property.

Alternatively, you can also use the classList property to add/remove classes to an element, like this:

<div class="alert info" id="myDiv">Important piece of information!</div>
 
 <script>
 // Selecting element
 var elem = document.getElementById("myDiv");     
 elem.classList.add("highlight");  // Add a highlight class
 elem.classList.remove("alert");  // Remove alert class
 </script>

The classList property is supported in all modern browsers. Not supported in IE prior to version 10.


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