Here's a simpler method to add multiple classes via classList
(supported by all modern browsers, as noted in other answers here):
div.classList.add('foo', 'bar'); // add multiple classes
From:
https://developer.mozilla.org/en-US/docs/Web/API/Element/classList#Examples
If you have an array of class names to add to an element, you can use the ES6 spread operator to pass them all into classList.add()
via this one-liner:
let classesToAdd = [ 'foo', 'bar', 'baz' ];
div.classList.add(...classesToAdd);
Note that not all browsers support ES6 natively yet, so as with any other ES6 answer you'll probably want to use a transpiler like Babel, or just stick with ES5 and use a solution like @LayZee's above.
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