参考博客：https://blog.csdn.net/blog_szhao/article/details/50220181
https://dojotoolkit.org/documentation/tutorials/1.10/promises/
Deferred是一个绝妙又给力的东西，但是它其实是更棒的promis的实现，dojo/Deferred 模块是promise在Dojo的主要实现方式
promise有以下特点：
- 可以为三个状态中的一个：unfulfilled、resolved、 rejected
- 可以从unfulfilled转变到resolved或者rejected
- 实现了一个 then 方法来针对状态改变的通知注册回调
- 回调不能改变promise产生的值
- promise的 then 方法返回一个新的promise，在保持原promise的值不变的情况下提供链式操作
举个栗子：
1 <!DOCTYPE HTML> 2 <html lang="en"> 3 <head> 4 <Meta charset="utf-8"> 5 <title>Demo: dojo/Deferred</title> 6 <link rel="stylesheet" href="style.css" media="screen"> 7 </head> 8 <body> 9 <h1>Demo: dojo/Deferred</h1> 10 <ul id="userlist"></ul> 11 <!-- load dojo and provide config via data attribute --> 12 <script src="//ajax.googleapis.com/ajax/libs/dojo/1.10.4/dojo/dojo.js" data-dojo-config="isDebug: 1,async: 1,parSEOnLoad: 1"></script> 13 <script> 14 require(["dojo/Deferred","dojo/request","dojo/_base/array","dojo/dom-construct","dojo/dom","dojo/domReady!"],15 function(Deferred,request,arrayUtil,domConstruct,dom) { 16 /*var deferred = new Deferred(),17 userlist = dom.byId("userlist"); 18 19 deferred.then(function(res){ 20 arrayUtil.forEach(res,function(user){ 21 domConstruct.create("li",{ 22 id: user.id,23 innerHTML: user.username + ": " + user.name 24 },userlist); 25 }); 26 },function(err){ 27 domConstruct.create("li",{ 28 innerHTML: "Error: " + err 29 },userlist); 30 }); 31 32 // Send an HTTP request 33 request.get("users.json",{ 34 handleAs: "json"}).then( 35 function(response){ 36 // Resolve when content is received 37 deferred.resolve(response); 38 },39 function(error){ 40 // Reject on error 41 deferred.reject(error); 42 } 43 );*/ 44 45 //由于dojo/Deferred模块是Dojo的promise接口的主要实现，所以上面这个例子可以这样写： 46 var deferred = request.get("users.json",{ 47 handleAs: "json" 48 }); 49 deferred.then(function(res){ 50 var userlist = dom.byId("userlist"); 51 arrayUtil.forEach(res,function(user){ 52 domConstruct.create("li",{ 53 id: user.id,54 innerHTML: user.username + ": " + user.name 55 },userlist); 56 }); 57 },function(err){ 58 // This shouldn‘t occur,but it‘s defined just in case 59 alert("An error occurred: " + err); 60 }); 61 }); 62 </script> 63 </body> 64 </html>