Use duplicate class name on an element?

Question

I found that there are many frameworks that will check the duplicate class name before adding the new class name on the element which I think will slow down the performance. Are there any problems when the element has a duplicate class name? It will also apply the CSS class without conflict while the duplicate class name is in use. ```

``` Is it OK to add a class name simply just like `elem.className += ' ' + 'aa ee'`, even if the element has a duplicate class name?

Accepted Answer

There is nothing "wrong" with having a duplicate class name, it's just redundant. There's probably a small performance impact, but that'll only really make much difference if you have a lot of duplication.

Also, preventing duplicates just helps to keep things tidy.

Use duplicate class name on an element?

Solution

Problem