/*

 * pending:初始化成功

 * fulfilled:成功

 * rejected：失败

 * */

function Promise(executor) {// 执行器

    this.status = 'pending';

    this.value = undefined;

    this.reason = undefined;

    this.fulfilledCallback = [];

    this.rejectCallback = [];

    let resolve = (value)=>{

        if(this.status=='pending'){

            this.status = 'resolve';

            this.value = value;

            this.fulfilledCallback.forEach(fn=>fn())

        }

    };

    let reject = (reason)=>{

        if(this.status =='pending'){

            this.status = 'reject';

            this.reason = reason;

            this.rejectCallback.forEach(fn=>fn())

        }

    };

    try{

        executor(resolve,reject)

    }catch(e){

        reject(e)

    }

}

Promise.prototype.then = function (onfulfilled,onrejected) {

    if(this.status == 'resolve'){

        onfulfilled(this.value)

    }

    if(this.status == 'reject'){

        onrejected(this.reason)

    }

    if(this.status == 'pending'){

        this.fulfilledCallback.push(()=>{

            onfulfilled(this.value)

        });

        this.rejectCallback.push(()=>{

            onrejected(this.reason)

        })

    }

};

var a = new Promise((resolve,reject)=>{

    setTimeout(()=>{

        resolve(10)

    })

});

a.then((res)=>{

    console.log(res);

});