Wrap an element in a specified tag with specified classes, using vanilla JavaScript

wrapThis.js

/**
 * Wrap an element
 * @param elementToWrap - selector of element to wrap
 * @param elementToUse - HTML tag to use for the wrapper
 * @param classes - class(es) to add; accepts string or array
 * @returns {Node | *}
 */
function wrapThis(elementToWrap, elementToUse, classes) {
	var wrapper = document.createElement(elementToUse);
	elementToWrap.parentNode.appendChild(wrapper);
	console.log(typeof(classes));
	if(typeof(classes) == 'string') {
		wrapper.classList.add(classes);
	} else { // It's an array
		for (var i = 0; i < classes.length; i++) {
			wrapper.classList.add(classes[i]);
		}
	}
	return wrapper.appendChild(elementToWrap);
};

wrapThisExample.js

/**
 * Add wrappers to YouTube and Vimeo embeds
 * @uses wrapThis()
 */
// Select all the embeds
var embeds = document.querySelectorAll('iframe[src*="youtube.com"], iframe[src*="vimeo.com"]'), i;
// Define classes. Must be an array/object if sending multiple classes; can use a string if only sending one class
var classes = ['responsive-embed', 'widescreen'];
// Loop through all the embeds and run the wrapThis() function on each
for (i = 0; i < embeds.length; i++) {
	wrapThis(embeds[i], 'div', classes);
}