// basically, of before:
var youtubeDiv = document.querySelector('iframe[src="http://www.youtube.com/embed/Jk5lTqQzoKA"]')

// after     
var youtubeDiv = document.querySelector('iframe[src^="http://www.youtube.com"]');
// or even, for my needs
var youtubeDiv = document.querySelector('iframe[src*="youtube"]');