jQuery addClass() Method

Add a class name to the first <p> element:

$("button").click(function(){
$("p:first").addClass("intro");
});

Definition and Usage

The addClass() method adds one or more class names to the selected elements.

This method does not remove existing class attributes, it only adds one or more class names to the class attribute.

Tip: To add more than one class, separate the class names with spaces.

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

Parameter	Description
classname	Required. Specifies one or more class names to be added
function(index,currentclass)	Optional. Specifies a function that returns one or more class names to be added index - Returns the index position of the element in the set currentclass - Returns the current class name of the selected element

Add two classes to an element
How to add two class names to a specified element.

Add classes using a function
How to add classes to selected elements using a function.

Change the class name of an element
How to use addClass() and removeClass() to remove one class name, and add a new class name.