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var global = require('./_global')
, macrotask = require('./_task').set
, Observer = global.MutationObserver || global.WebKitMutationObserver
, process = global.process
, Promise = global.Promise
, isNode = require('./_cof')(process) == 'process';
module.exports = function(){
var head, last, notify;
var flush = function(){
var parent, fn;
if(isNode && (parent = process.domain))parent.exit();
while(head){
fn = head.fn;
head = head.next;
try {
fn();
} catch(e){
if(head)notify();
else last = undefined;
throw e;
}
} last = undefined;
if(parent)parent.enter();
};
// Node.js
if(isNode){
notify = function(){
process.nextTick(flush);
};
// browsers with MutationObserver
} else if(Observer){
var toggle = true
, node = document.createTextNode('');
new Observer(flush).observe(node, {characterData: true}); // eslint-disable-line no-new
notify = function(){
node.data = toggle = !toggle;
};
// environments with maybe non-completely correct, but existent Promise
} else if(Promise && Promise.resolve){
var promise = Promise.resolve();
notify = function(){
promise.then(flush);
};
// for other environments - macrotask based on:
// - setImmediate
// - MessageChannel
// - window.postMessag
// - onreadystatechange
// - setTimeout
} else {
notify = function(){
// strange IE + webpack dev server bug - use .call(global)
macrotask.call(global, flush);
};
}
return function(fn){
var task = {fn: fn, next: undefined};
if(last)last.next = task;
if(!head){
head = task;
notify();
} last = task;
};
};
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