简单实现一个Promise

class PromiseClone {
    constructor (process) {
        this.status = 'pending'
        this.msg = ''
        process(this.resolve.bind(this), this.reject.bind(this))
        return this
    }
    resolve (val) {
        this.status = 'fulfilled'
        this.msg = val
    }
    reject (err) {
        this.status = 'rejected'
        this.msg = err
    }
    then (fufilled, reject) {
        if(this.status === 'fulfilled') {
            fufilled(this.msg)
        }
        if(this.status === 'rejected') {
            reject(this.msg)
        }
    }

}
//测试代码
var mm=new PromiseClone(function(resolve,reject){
    resolve('123');
});
mm.then(function(success){
    console.log(success);
},function(){
    console.log('fail!');
});