Select and add class in javascript

Question

Cross Platform if possible, how can I select classes in Javascript (but not Jquery please -MooTools is fine though-) on code that I can\'t add an ID? Specifically, I want to add

Answer 1

I know this is old, but is there any reason not to simply do this (besides potential browser support issues)?

document.querySelectorAll("li.even, li.odd").forEach((el) => {
    el.classList.add('cf');
});

Support: https://caniuse.com/#feat=es5