获取<a> tag

Question

I'm working on a userscript for YouTube and I need to retrieve the href attribute of an <a> tag through the class name.

This was my attempt but it just returned "undefined":

var x = document.getElementsByClassName("mix-playlist").getAttribute("href");
console.log(x);

<a class="XY XY XY mix-playlist XY" href="XY"></a>

Thanks for your help!

Nevermind, I figured it out. I just had to move it into this function: document.addEventListener("DOMContentLoaded", function() {

and split the resulting array.

Sorry for the duplicate but I just couldn't gather much information after looking through stackoverflow questions for 20 minutes.