How do I add a class to a given element?

Question

I have an element that already has a class:

Answer 1

In my case, I had more than one class called main-wrapper in the DOM, but I only wanted to affect the parent main-wrapper. Using :first Selector (https://api.jquery.com/first-selector/), I could select the first matched DOM element. This was the solution for me:

$(document).ready( function() {
    $('.main-wrapper:first').addClass('homepage-redesign');
    $('#deals-index > div:eq(0) > div:eq(1)').addClass('doubleheaderredesign');
} );

I also did the same thing for the second children of a specific div in my DOM as you can see in the code where I used $('#deals-index > div:eq(0) > div:eq(1)').addClass('doubleheaderredesign');.

NOTE: I used jQuery as you can see.