本文共 1453 字，大约阅读时间需要 4 分钟。

class MyPromise{        constructor(callback){            this.status = 'pendding';            this.result = null;            this.err = null;            this.resolveFn = null;            this.rejectFn = null;            this.resolve = function(val){                if(this.status === 'pendding'){                    this.status = 'resolve';                    this.result = val;                    this.resolveFn && this.resolveFn(this.result);                }            }            this.reject = function(err){                if(this.status === 'pendding'){                    this.status = 'reject';                    this.err = err;                    this.rejectFn && this.rejectFn(this.err);                }            }            callback(this.resolve.bind(this),this.reject.bind(this));          }        then(callback){            if(this.status === 'resolve' ){                callback(this.result);            }else{                this.resolveFn = callback;            }            return this;        }        catch(callback){            if(this.status === 'reject' ){                callback(this.err);            }else{                this.rejectFn = callback;            }        }      }

 调用

let p = new MyPromise((resolve,reject) => {        setTimeout(() => {            resolve(123);            reject(456);          },1000)      })    p.then(res => {        console.log(res);    }).catch(err => {        console.log(err);    })

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