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- 'use strict';
- var Mutation = global.MutationObserver || global.WebKitMutationObserver;
- var scheduleDrain;
- {
- if (Mutation) {
- var called = 0;
- var observer = new Mutation(nextTick);
- var element = global.document.createTextNode('');
- observer.observe(element, {
- characterData: true
- });
- scheduleDrain = function () {
- element.data = (called = ++called % 2);
- };
- } else if (!global.setImmediate && typeof global.MessageChannel !== 'undefined') {
- var channel = new global.MessageChannel();
- channel.port1.onmessage = nextTick;
- scheduleDrain = function () {
- channel.port2.postMessage(0);
- };
- } else if ('document' in global && 'onreadystatechange' in global.document.createElement('script')) {
- scheduleDrain = function () {
- // Create a <script> element; its readystatechange event will be fired asynchronously once it is inserted
- // into the document. Do so, thus queuing up the task. Remember to clean up once it's been called.
- var scriptEl = global.document.createElement('script');
- scriptEl.onreadystatechange = function () {
- nextTick();
- scriptEl.onreadystatechange = null;
- scriptEl.parentNode.removeChild(scriptEl);
- scriptEl = null;
- };
- global.document.documentElement.appendChild(scriptEl);
- };
- } else {
- scheduleDrain = function () {
- setTimeout(nextTick, 0);
- };
- }
- }
- var draining;
- var queue = [];
- //named nextTick for less confusing stack traces
- function nextTick() {
- draining = true;
- var i, oldQueue;
- var len = queue.length;
- while (len) {
- oldQueue = queue;
- queue = [];
- i = -1;
- while (++i < len) {
- oldQueue[i]();
- }
- len = queue.length;
- }
- draining = false;
- }
- module.exports = immediate;
- function immediate(task) {
- if (queue.push(task) === 1 && !draining) {
- scheduleDrain();
- }
- }
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