async-await

async, await and promise not conflict, it may be an extension of promise

1, then just a split callback (previously callbak is also a function, but can split the back, of the assembly)

 

function WaitHandle () {
　　var DTD .Deferred = $ (); // Create a deferred objects 

　　var the wait = function (DTD) { // requires a passing object is deferred 
　　　　var Task = function () { 
　　　　　　the console.log ( 'execution completion ' ); 
　　　　　　dtd.resolve (); // for asynchronous task has been completed 
　　　　　　// dtd.reject (); // indicating an asynchronous tasks fail or error 
　　　　} 
　　　　the setTimeout (task, 2000 );
　　　　return dtd.promise (); // where Back Promise, rather than directly go back deferreds 
　　} 

　　// Note that this value must be returned 
　　return the wait (DTD); 
}

var w = waitHandle();
w.then(function(){
　　console.log('ok1')
},function(){
　　console.log('error1')
}).then(function(){
　　console.log('ok2')
},function(){
　　console.log('error2');
})

 

 

2, aysnc / await it is the most direct synchronization wording (of the order of execution with the same wording)

 

import 'babel-polyfill';
function loadImg(src) {
　　const promise = new Promise(function (resolve, reject) {
　　　　var img = document.createElement('img');
　　　　img.onload = function(){
　　　　　　resolve(img);
　　　　}
　　　　img.onerror = function(){
　　　　　　reject();
　　　　}
　　　　img.src = src;
　　})
　　return promise;
}

const load = async function(){
　　const result1 = await loadImg('xxx.png');
　　console.log(result1);
　　const result2 = await loadImg('yyy.png');
　　console.log(result2);
}
load();

 

usage

1, the await use, the function must be identified async

2, await followed example is a Promise

3, need babel-polyfill (meaning compatible)

npm i --save-dev babel-polyfill

 

to sum up

1, a Promise, and there is no conflict and Promise

2, the wording is completely synchronized, no callback function

3, however: js not change the nature of single-threaded, asynchronous