Promise简单实现

function Promise(fn)
{
    this._resolvefun=null;
    this._rejectfun=null;
    this.status="pending";
    this.value="";
    this.reason="";
    var bind=function(ctx,fun){
      return function(){
        fun.apply(ctx,arguments);
      }
    }
    fn(bind(this,this.resolve), bind(this,this.reject));
}
Promise.prototype["resolve"]=function(value){
        if(this.status!="pending") return;
        this.status="fulfilled";
        this.value=value;
        this._resolvefun&&this._resolvefun(this.value);
}

Promise.prototype["reject"]=function(reason){
        if(this.status!="pending") return;
        this.status="rejected";
        this.reason=reason;
        this._rejectfun&&this._rejectfun(this.reason);
}

Promise.prototype["then"]=function(onFulfilled, onRejected){
        if(this.status!="pending") return;
        this._resolve=onFulfilled;
        this._reject=onRejected;
        return this;
}

new Promise(function(resolve, reject) {
    console.log("b");
 //setTimeout(resolve, 10, 'done');
 setTimeout(reject, 10, 'done');
 }).then((value) => {
  console.log(value);
},(value) => {
  console.log(value);
});