promise手寫源碼

class PromiseNew{
    constructor(fn){
        this.satate="PENDING"
        this.doneList = []
        this.failList = []
        fn(this.resolve.bind(this) ,this.reject.bind(this))  //fn是外部函數，裏面this已經改變，所以要綁定bind
    }
    done(handle){
        if(typeof  handle ==="function"){
            this.doneList.push(handle)
        }else{
            throw new Error("缺少回調函數")
        }
        return this
    }
    fail(handle){
        if(typeof  handle ==="function"){
            this.failList.push(handle)
        }else{
            throw new Error("缺少回調函數")
        }
        return this
    }
    then(success,fail){
        this.done(success  || function(){}).fail(fail || function(){})
        return this
    }

    resolve () {
        this.satate="RESOLVED"
        let args =Array.prototype.slice.call(arguments)
        setTimeout(function(){
            this.doneList.forEach((item, key) => {
                let arg = item.apply(null,args)  //實際上doneList中第一個函數的返回值是第二個函數的參數
                args = [] //清空參數
                args.push(arg)
            });
            this.doneList =[] //清空數據
        }.bind(this), 200)
        return this
    }
    reject(){
        this.satate="REJECTED"
        let args =Array.prototype.slice.call(arguments)
        setTimeout(function(){
            this.failList.forEach((item, key) => {
                let arg = item.apply(null,args)
                args = [] 
                args.push(arg)
            });
            this.failList =[] //清空數據
        }.bind(this), 200)
        console.log("reject 執行")
    }
}
new PromiseNew((resolve,reject)=>{
    resolve("啪啪啪")
    reject()
    console.log("ben")
}).then((value)=>{
    console.log("success",value)
    return 9999
},()=>{
    console.log("fail")
})