1 function Promise(fn)
 2 {
 3     this._resolvefun=null;
 4     this._rejectfun=null;
 5     this.status="pending";
 6     this.value="";
 7     this.reason="";
 8     var bind=function(ctx,fun){
 9       return function(){
10         fun.apply(ctx,arguments);
11       }
12     }
13     fn(bind(this
 
,this.resolve), bind(this,this.reject));
14 }
15 Promise.prototype["resolve"]=function(value){
16         if(this.status!="pending") return;
17         this.status="fulfilled";
18         this.value=value;
19         this._resolvefun&&this._resolvefun(this.value);
20 }
21 
22 Promise.prototype["reject"]=function
 
(reason){
23         if(this.status!="pending") return;
24         this.status="rejected";
25         this.reason=reason;
26         this._rejectfun&&this._rejectfun(this.reason);
27 }
28 
29 Promise.prototype["then"]=function(onFulfilled, onRejected){
30         if(this.status!="pending") return
 
;
31         this._resolve=onFulfilled;
32         this._reject=onRejected;
33         return this;
34 }
35 
36 new Promise(function(resolve, reject) {
37     console.log("b");
38  //setTimeout(resolve, 10, ‘done‘);
39  setTimeout(reject, 10, ‘done‘);
40  }).then((value) => {
41   console.log(value);
42 },(value) => {
43   console.log(value);
44 });

Promise簡單實現