setAsap.js

(function (thisVar, undefined) {
	'use strict';
	var main = (typeof window === 'object' && window) || (typeof global === 'object' && global) ||
		typeof self === 'object' && self || thisVar;

	var hasSetImmediate = typeof setImmediate === 'function';
	var hasNextTick = typeof process === 'object' && !!process && typeof process.nextTick === 'function';
	var index = 0;

	function getNewIndex() {
		if (index === 9007199254740991) {
			return 0;
		}
		return ++index;
	}

	var setAsap = (function () {
		var hiddenDiv, scriptEl, timeoutFn, callbacks;

		// Modern browsers, fastest async
		if (main.MutationObserver) {
			return function setAsap(callback) {
				hiddenDiv = document.createElement("div");
				(new MutationObserver(function() {
					callback();
					hiddenDiv = null;
				})).observe(hiddenDiv, { attributes: true });
				hiddenDiv.setAttribute('i', '1');
			};

		// Browsers that support postMessage
		} else if (!hasSetImmediate && main.postMessage && !main.importScripts && main.addEventListener) {

			var MESSAGE_PREFIX = "com.setImmediate" + Math.random();
			callbacks = {};

			var onGlobalMessage = function (event) {
				if (event.source === main && event.data.indexOf(MESSAGE_PREFIX) === 0) {
					var i = +event.data.split(':')[1];
					callbacks[i]();
					delete callbacks[i];
				}
			};

			main.addEventListener("message", onGlobalMessage, false);

			return function setAsap(callback) {
				var i = getNewIndex();
				callbacks[i] = callback;
				main.postMessage(MESSAGE_PREFIX + ':' + i, "*");
			};

			// IE browsers without postMessage
		} else if (!hasSetImmediate && main.document && 'onreadystatechange' in document.createElement('script')) {

			return function setAsap(callback) {
				scriptEl = document.createElement("script");
				scriptEl.onreadystatechange = function onreadystatechange() {
					scriptEl.onreadystatechange = null;
					scriptEl.parentNode.removeChild(scriptEl);
					scriptEl = null;
					callback();
				};
				document.body.appendChild(scriptEl);
			};

		// All other browsers and node
		} else {

			timeoutFn = (hasSetImmediate && setImmediate) || (hasNextTick && process.nextTick) || setTimeout;
			return function setAsap(callback) {
				timeoutFn(callback);
			};
		}

	})();

	if (typeof module !== 'undefined' && module.exports) {
		module.exports = setAsap;
	} else if (typeof require !== 'undefined' && require.amd) {
		define(function () {
			return setAsap;
		});
	} else {
		main.setAsap = setAsap;
	}
})(this);