when/lib/env.js

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

/*global process,document,setTimeout,clearTimeout,MutationObserver,WebKitMutationObserver*/
(function(define) { 'use strict';
define(function(require) {
	/*jshint maxcomplexity:6*/

	// Sniff "best" async scheduling option
	// Prefer process.nextTick or MutationObserver, then check for
	// setTimeout, and finally vertx, since its the only env that doesn't
	// have setTimeout

	var MutationObs;
	var capturedSetTimeout = typeof setTimeout !== 'undefined' && setTimeout;

	// Default env
	var setTimer = function(f, ms) { return setTimeout(f, ms); };
	var clearTimer = function(t) { return clearTimeout(t); };
	var asap = function (f) { return capturedSetTimeout(f, 0); };

	// Detect specific env
	if (isNode()) { // Node
		asap = function (f) { return process.nextTick(f); };

	} else if (MutationObs = hasMutationObserver()) { // Modern browser
		asap = initMutationObserver(MutationObs);

	} else if (!capturedSetTimeout) { // vert.x
		var vertxRequire = require;
		var vertx = vertxRequire('vertx');
		setTimer = function (f, ms) { return vertx.setTimer(ms, f); };
		clearTimer = vertx.cancelTimer;
		asap = vertx.runOnLoop || vertx.runOnContext;
	}

	return {
		setTimer: setTimer,
		clearTimer: clearTimer,
		asap: asap
	};

	function isNode () {
		return typeof process !== 'undefined' &&
			Object.prototype.toString.call(process) === '[object process]';
	}

	function hasMutationObserver () {
	    return (typeof MutationObserver !== 'undefined' && MutationObserver) ||
			(typeof WebKitMutationObserver !== 'undefined' && WebKitMutationObserver);
	}

	function initMutationObserver(MutationObserver) {
		var scheduled;
		var node = document.createTextNode('');
		var o = new MutationObserver(run);
		o.observe(node, { characterData: true });

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

		var i = 0;
		return function (f) {
			scheduled = f;
			node.data = (i ^= 1);
		};
	}
});
}(typeof define === 'function' && define.amd ? define : function(factory) { module.exports = factory(require); }));