How to find a specific class name of element when there are multiple classes?

Question

I have some DIVs on a page. Each has 3 classes: grid_#, push_# and pull_# where # is an actual number.

I need to replace each class separately, i.e. r

Answer 1

If element has multiple classes, you need to use split:

var old = document.getElementById('elementId');
var old_class = old.className.split(' ')[0]; // first class

What split does is that it creates an array by splitting string (class in this case) which you can later access by its index eg [0] for first class.

If element has just one class, you simply use className:

var cls = old.className;