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本文有参考其他文章，不过地址忘了~~~。
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上代码
const PROMISE_STATUS = { PENDING: 'PENDING', FULFILLED: 'FULFILLED', REJECTED: 'REJECTED'}class ModelPromise { static promiseId = 1; constructor(initFn) { if (typeof initFn !== 'function') { throw new Error('must be function') } this.promiseId = ModelPromise.promiseId; this.promiseStatus = PROMISE_STATUS.PENDING; this.promiseValue = undefined; this.onFulfilledStack = []; this.onRejectStack = []; this.finallyCallback = undefined; initFn(this._resolve.bind(this), this._reject.bind(this)); ModelPromise.promiseId++; } _resolve(resolveValue) { if (this.promiseStatus !== PROMISE_STATUS.PENDING) { return; } const runFulfilled = (value) => { let onFulfilled; while (onFulfilled = this.onFulfilledStack.shift()) { onFulfilled(value); } if (this.finallyCallback) { this.finallyCallback()} } const runRejected = (error) => { let onReject; while (onReject = this.onRejectStack.shift()) { onReject(error); } if (this.finallyCallback) { this.finallyCallback()} } const run = () => { if (resolveValue instanceof ModelPromise) { // 有父子依赖关系时候父值将由子值决定 resolveValue.then((value) => { this.promiseStatus = PROMISE_STATUS.FULFILLED; this.promiseValue = value; runFulfilled(value); }, (err) => { this.promiseStatus = PROMISE_STATUS.REJECTED; this.promiseValue = err; runRejected(err); }); } else { this.promiseStatus = PROMISE_STATUS.FULFILLED; this.promiseValue = resolveValue; runFulfilled(resolveValue); } } setTimeout(run); } _reject(err) { if (this.promiseStatus !== PROMISE_STATUS.PENDING) { return; } const run = () => { this.promiseStatus = PROMISE_STATUS.REJECTED; this.promiseValue = err; let onReject; while (onReject = this.onRejectStack.shift()) { onReject(error); } } setTimeout(run); } then(onFulfill, onReject) { let _resolveNext; let _rejectNext; /* 生成一个新的promise等待返回 */ let newPromise = new ModelPromise((resolve, reject) => { _resolveNext = resolve; _rejectNext = reject; }); const runFulfilled = value => { try { if (typeof onFulfill !== 'function') { _resolveNext(value); } else { let onFulfillReturn = onFulfill(value); if (onFulfillReturn instanceof ModelPromise) { onFulfillReturn.then(_resolveNext, _rejectNext); } else { _resolveNext(onFulfillReturn); } } } catch(err) { _rejectNext(err); } } const runRejected = error => { try { if (typeof onReject !== 'function') { _resolveNext(value); } else { let onRejectedReturn = onReject(error); if (onRejectedReturn instanceof ModelPromise) { onRejectedReturn.then(_resolveNext, _rejectNext); } else { _rejectNext(onRejectedReturn); } } } catch(err) { _rejectNext(err); } } if (this.promiseStatus === PROMISE_STATUS.FULFILLED) { runFulfilled(this.promiseValue); } else if (this.promiseStatus === PROMISE_STATUS.REJECTED) { runRejected(this.promiseValue); } else { /* important！！！！ */ /* 此时推入栈中待执行的不是onFulfill， 而是runFulfilled */ /* 核心需要关注的是，当一个函数在resolve之后，应当执行then函数的回调函数并且返回值赋值给下一个promise，_resolveNext(onRejectedReturn); */ this.onFulfilledStack.push(runFulfilled); this.onRejectStack.push(runRejected); } return newPromise; } catch (catchFn) { this.then(undefined, catchFn); } finally(finallyCallback) { this.finallyCallback = finallyCallback; } static resolve(value) { // 如果需要处理的本身就是一个promise，则直接返回使用这个promise if (value instanceof ModelPromise) return value; let newPromise = new ModelPromise(resolve => { resolve(value); }); return newPromise; } static reject(value) { let newPromise = new ModelPromise(resolve, reject => { reject(value); }); return newPromise; } static race(promiseArr) { let newPromise = new ModelPromise((resolve, reject) => { promiseArr.forEach((item, index) => { if (item instanceof ModelPromise) { item.then(res => { resolve(res); checkAllResolve(); }, err => { reject(err); }); } else { resolve(item); } }); }); return newPromise; } static all(promiseArr) { let newPromise = new ModelPromise((resolve, reject) => { let promiseValArr = []; //保存所有promise的value，按顺序； const checkAllResolve = () => { if (promiseValArr.length === promiseArr.length) { resolve(promiseValArr); } } promiseArr.forEach((item, index) => { promiseValArr[index] = undefined; if (item instanceof ModelPromise) { item.then(res => { promiseValArr[index] = res; checkAllResolve(); }, err => { reject(err); }); } else { promiseValArr[index] = item; checkAllResolve(); } }); }); return newPromise; }}/* test start */let p1 = new ModelPromise((resolve, reject) => { console.log("同步执行"); setTimeout(() => { resolve('第一次resolve的值'); console.log(p1); console.log(p2); console.log(p3); console.log(p4); console.log(p5); }, 1000);});let p2 = p1.then((res) => { console.log('after then1', res); return new ModelPromise((resolve, reject) => { resolve('新promise的返回值'); });})let p3 = p2.then((res) => { console.log('after then2', res); return new ModelPromise((resolve, reject) => { setTimeout(() => { resolve('3S 后再执行的结果'); }, 3000); });});// console.log(promise1);let p4 = p1.then((res) => { console.log('接收到第一次resolve的值', res); return '第二次then的返回值';});// console.log(promise2);let p5 = p3.then((res) => { console.log('接收到第二次resolve的值', res);}).catch((err) => { console.log('捕获错误', err);});/* let promiseAll = ModelPromise.all([p1, p2, p3]).then(res => { console.log('promiseAll', res);}); */let promiseAll = ModelPromise.race([p1, p2, p3]).then(res => { console.log('promise race', res);});promiseAll.finally(() => { console.log('promiseAll finally');});