/** * Created by wyw on 2019/5/3. */ const PENDING = 'pending'; const FULFILLED = 'fulfilled'; const REJECTED = 'rejected'; function Promise(executor) { let self = this; self.status = PENDING; self.onFulfilled = [];//成功的回调 self.onRejected = []; //失败的回调 //PromiseA+ 2.1 function resolve(value) { if (self.status === PENDING) { self.status = FULFILLED; self.value = value; console.log(self.onFulfilled) self.onFulfilled.forEach(fn => fn());//PromiseA+ 2.2.6.1 } } function reject(reason) { if (self.status === PENDING) { self.status = REJECTED; self.reason = reason; self.onRejected.forEach(fn => fn());//PromiseA+ 2.2.6.2 } } try { executor(resolve, reject); } catch (e) { reject(e); } } Promise.prototype.then = function (onFulfilled, onRejected) { //PromiseA+ 2.2.1 / PromiseA+ 2.2.5 / PromiseA+ 2.2.7.3 / PromiseA+ 2.2.7.4 onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : value => value; onRejected = typeof onRejected === 'function' ? onRejected : reason => { throw reason }; let self = this; //PromiseA+ 2.2.7 let promise2 = new Promise((resolve, reject) => { if (self.status === FULFILLED) { //PromiseA+ 2.2.2 //PromiseA+ 2.2.4 --- setTimeout setTimeout(() => { try { //PromiseA+ 2.2.7.1 let x = onFulfilled(self.value); resolvePromise(promise2, x, resolve, reject); } catch (e) { //PromiseA+ 2.2.7.2 reject(e); } }); } else if (self.status === REJECTED) { //PromiseA+ 2.2.3 setTimeout(() => { try { let x = onRejected(self.reason); resolvePromise(promise2, x, resolve, reject); } catch (e) { reject(e); } }); } else if (self.status === PENDING) { self.onFulfilled.push(() => { setTimeout(() => { try { let x = onFulfilled(self.value); resolvePromise(promise2, x, resolve, reject); } catch (e) { reject(e); } }); }); self.onRejected.push(() => { setTimeout(() => { try { let x = onRejected(self.reason); resolvePromise(promise2, x, resolve, reject); } catch (e) { reject(e); } }); }); } }); return promise2; } function resolvePromise(promise2, x, resolve, reject) { let self = this; //PromiseA+ 2.3.1 if (promise2 === x) { reject(new TypeError('Chaining cycle')); } if (x && typeof x === 'object' || typeof x === 'function') { let used; //PromiseA+2.3.3.3.3 只能调用一次 try { let then = x.then; if (typeof then === 'function') { //PromiseA+2.3.3 then.call(x, (y) => { //PromiseA+2.3.3.1 if (used) return; used = true; resolvePromise(promise2, y, resolve, reject); }, (r) => { //PromiseA+2.3.3.2 if (used) return; used = true; reject(r); }); }else{ //PromiseA+2.3.3.4 if (used) return; used = true; resolve(x); } } catch (e) { //PromiseA+ 2.3.3.2 if (used) return; used = true; reject(e); } } else { //PromiseA+ 2.3.3.4 resolve(x); } } Promise.resolve = function (param) { if (param instanceof Promise) { return param; } return new Promise((resolve, reject) => { if (param && param.then && typeof param.then === 'function') { setTimeout(() => { param.then(resolve, reject); }); } else { resolve(param); } }); } Promise.reject = function (reason) { return new Promise((resolve, reject) => { reject(reason); }); } Promise.prototype.finally = function (callback) { return this.then((value) => { return Promise.resolve(callback()).then(() => { return value; }); }, (err) => { return Promise.resolve(callback()).then(() => { throw err; }); }); } Promise.prototype.catch = function (onRejected) { return this.then(null, onRejected); } // let p = new Promise((resolve, reject) => { // resolve(1) // }).then(r => console.log(r)); // new Promise((resolve, reject) => { // reject(1) // }).then(r => { // return 2; // }, err => { // return 3; // }).finally(() => { // console.log(3333) // }).then(c => { // console.log('22222', c); // }); // 和原生promise表现不一致 原生只输出 hehe // new Promise((resolve, reject) => { // resolve(new Promise((resolve, reject) => { // reject('hehe'); // })); // }).then(r => { // console.log(1111) // }).then(r => { // console.log(r); // }).catch(err => { // console.log(err); // })