/** * Created by wyw on 2018/12/17. */ function Promise(Fn){ this.value; this.reason; this.resolves = []; this.rejects = []; this.status = 'PENDING'; if(this.status === 'PENDING') { let transition = (status, val) => { setTimeout(_ => { this.status = status; let f = status === 'FULFILLED', queue = this[f ? 'resolves' : 'rejects']; queue.forEach(fn => val = fn(val) || val); this[f ? 'value' : 'reason'] = val; }); }; var resolve = (value) => { transition('FULFILLED', value); }; var reject = (reason) => { transition('REJECTED', reason); } } try { Fn(resolve, reject); } catch(err) { reject(err); } } Promise.prototype.then = function(onFulfilled, onRejected) { let promise = this; return new Promise((resolve, reject) => { function success(value) { let val = typeof onFulfilled === 'function' && onFulfilled(value) || value; if(val && typeof val['then'] === 'function'){ // 判断是否有then方法 val.then(function(value){ // 如果返回的是Promise 则直接执行得到结果后再调用后面的then方法 resolve(value); },function(reason){ reject(reason); }); }else{ resolve(val); } } function erro (reason) { let rea = typeof onRejected === 'function' && onRejected(reason) || reason; reject(rea); } if (promise.status === 'PENDING') { promise.resolves.push(success); promise.rejects.push(erro); } else if (promise.status === 'FULFILLED') { success(promise.value); } else if (promise.status === 'REJECTED') { erro(promise.reason); } }); }; Promise.prototype.catch = function(onRejected){ return this.then(null, onRejected); }; // function getInfo(success, fail) { // return new Promise((resolve, reject) => { // setTimeout(_ => { // let ran = Math.random(); // console.log(success, ran); // if (ran > 0.5) { // resolve(success); // } else { // reject(fail); // } // }, 200); // }) // } // // getInfo('Vchat', 'fail').then(res => { // console.log('1', res); // return getInfo('可以线上预览了', 'erro'); // }).catch(err => { // console.log('2', err); // }).then(res => { // console.log('3', res); // }).catch(err => { // console.log('4', err); // }); const p2 = new Promise((resolve, reject) => { throw new Error('报错了'); }) .then(result => {console.log(result)}) .catch(e => { console.log(e); });