How to dynamically change CSS class of DIV tag?

Question

I am using JavaScript. I have a variable var boolVal that either evaluates to true/false. On my page, I have a div tag.

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Answer 1

First of all, AddClass is not a pure Javascript method. It's related to jQuery.

You can use Javascript for adding a class:

setAttribute and className both method are used to set class (class attribute), these method are not used to adding another class with existing one.

document.getElementById('div1').setAttribute( "class", "blueClass" );

OR

document.getElementById('div1').className="redClass";

Demo Fiddle

So if you want append a css class to an element, you can do it like this -

 document.getElementById('div1').setAttribute( "class", document.getElementById('div1').getAttribute('class') + " blueClass" );

OR

 document.getElementById('div1').className +=" redClass";

Note: Using this way, the same class can be added multiple times. It's only a trick to do this work using javascript, it's not a perfect solution

OR simply use jQuery to add class -

$("#div1").addClass("blueClass");

Working Fiddle