Determine the name of the `transtitionend` event

transitionend.js

	var NO_TRANSITIONS = 'no-transitions';
	/**
	 * This method tries to determine the name of the transitionend event, it
	 * could be the user's browser is using a prefixed version
	 */
	function getTransitionEndEventName () {
		// 1: The variable we use to keep track of the current key when
		//    iterating over the transitions object
		// 2: An element we can use to test if a CSS property if known to the
		//    browser
		// 3: The key:value pairs represent CSS-property:Event-name values. By
		//    testing if the browser supports a CSS property we can tell what
		//    name to use for the transitionend event
		// 4: oTransitionEnd in very old Opera
		var key,                                                       /* [1] */
		    el = document.createElement('div'),                        /* [2] */
		    transitions = {                                            /* [3] */
			    WebkitTransition : 'webkitTransitionEnd',
			    OTransition      : 'otransitionend',                   /* [4] */
			    MozTransition    : 'transitionend',
			    transition       : 'transitionend'
			};

		// Loop over the keys in the transition object
		for (key in transitions) {
			// Check the key is a property of the object and check if the CSS
			// property does not return undefined. If the result is undefined it
			// means the browser doesn't recognize the (un)prefixed property
			if (transitions.hasOwnProperty(key) && el.style[key] !== undefined) {
				// The CSS property exists, this means we know which name of the
				// transitionend event we can use for this browser
				return transitions[key];
			}
		}

		// If the method reaches this line it means that none of the CSS
		// properties were recognized by the browser. It is safe to conclude
		// there is no support for transitions (or at least none that we can use
		// in any meaningful way)
		return NO_TRANSITIONS;
	}