jQuery addClass() Method Tutorial

Last Updated: June 4, 2021

The jQuery addClass() method is used to add one or more CSS class to a selected element/elements. To add more than one class name, separate them using spaces.

Syntax of jQuery addClass

1	`$(selector).addClass(classname,function(index,currentclass))`

Parameter	Description
classname	Required Parameter: names of the classes to be added to the selector
function(index,currentClass)	Optional Parameter: A function that returns one or more class names that are spaces-separated. The returned class names are added to the selector. index: index position of the element in the selector. currentClass: current class names of the element in the selector.

Related to jQuery addClass Methods

jQuery hasClass method tutorial.
jQuery removeClass method tutorial.

Example 1: Add a Single Class Name

I have a paragraph element to which I will apply CSS Class called red.

<style>
.red {
    color: Red;
}
</style>
  
<p id="myParagraph">My Paragraph</p>
<button id="myButton">Add Class</button>

On the button Click I use the jQuery addClass like this:

$("#myButton").click(function (e) {
    $("#myParagraph").addClass("red");
});

This will add the red Class to the paragraph and it’s color changes to Red.

Example 2: Add 3 Class Names

I can add more than one CSS Class to the selector using jQuery addClass method. Here I add 3 Classes to the paragraph element, these classes are red, fontBold and borderSolid.

<style>
.red {
    color: Red;
}
  
.fontBold {
    font-weight: bold;
}
  
.borderSolid {
    border: solid 1px #4CAF50;
}
</style>
  
<p id="myParagraph">My Paragraph</p>
<button id="myButton">Add 3 Class</button>

The jQuery code:

$("#myButton").click(function (e) {
    $("#myParagraph").addClass("red fontBold borderSolid");
});

In the jQuery addClass method each of the 3 class names are separated by a space. So on the button click the myParagraph element will become – Red in color, with font weight bold and a solid border.

Example 3: Using jQuery addClass Function Parameter

The CSS Class names returned by the addClass() function parameter, are applied to the selector. Let me show you how to use this function.

I have 3 paragraph element, 2 already have red class while the 3rd does not contain any class. Now I want to add borderSolid class to the paragraph whose index is ‘not 0’ and does not contain the red class.

<style>
.red {
    color: Red;
}
  
.borderSolid {
    border: solid 1px #4CAF50;
}
</style>
  
<p class="red">First Paragraph with class "Red"</p>
<p class="red">Second Paragraph with class "Red"</p>
<p>Third Paragraph without any class</p>
  
<button id="myButton">Add Class</button>

The jQuery addClass code will be:

$("#myButton").click(function (e) {
    $("p").addClass(function (index, currentClass) {
        if (index != 0 && currentClass == "red")
            return "borderSolid";
    });
});