when/lib/async.js

/** @license MIT License (c) copyright 2010-2014 original author or authors */
/** @author Brian Cavalier */
/** @author John Hann */

(function(define) { 'use strict';
define(function(require) {

	// Sniff "best" async scheduling option
	// Prefer process.nextTick or MutationObserver, then check for
	// vertx and finally fall back to setTimeout

	/*jshint maxcomplexity:6*/
	/*global process,document,setTimeout,MutationObserver,WebKitMutationObserver*/
	var nextTick, MutationObs;

	if (typeof process !== 'undefined' && process !== null &&
		typeof process.nextTick === 'function') {
		nextTick = function(f) {
			process.nextTick(f);
		};

	} else if (MutationObs =
		(typeof MutationObserver === 'function' && MutationObserver) ||
		(typeof WebKitMutationObserver === 'function' && WebKitMutationObserver)) {
		nextTick = (function (document, MutationObserver) {
			var scheduled;
			var el = document.createElement('div');
			var o = new MutationObserver(run);
			o.observe(el, { attributes: true });

			function run() {
				var f = scheduled;
				scheduled = void 0;
				f();
			}

			return function (f) {
				scheduled = f;
				el.setAttribute('class', 'x');
			};
		}(document, MutationObs));

	} else {
		nextTick = (function(cjsRequire) {
			try {
				// vert.x 1.x || 2.x
				return cjsRequire('vertx').runOnLoop || cjsRequire('vertx').runOnContext;
			} catch (ignore) {}

			// capture setTimeout to avoid being caught by fake timers
			// used in time based tests
			var capturedSetTimeout = setTimeout;
			return function (t) {
				capturedSetTimeout(t, 0);
			};
		}(require));
	}

	return nextTick;
});
}(typeof define === 'function' && define.amd ? define : function(factory) { module.exports = factory(require); }));