How to add class to element only if it already does not have it?

Question

How to add a class to an element only if it already does not have it? Say we don't know if the element has class="desired_class ... but we want to make sure it has.

Answer 1

Also, you can use classList property and it's add() method:

var element = document.getElementById('myElement');
element.classList.add('myClass');

The class name will be added only if the element does not have it.

More about classList: https://developer.mozilla.org/en-US/docs/Web/API/Element/classList

Answer 2

try this

var elem = $('selector');
if(!elem.hasClass('desired_class')){
  elem.addClass('desired_class');
 }