试图写了一下,大概测试了一下,没有用专业的测试工具测试....
代码感觉还是写的比较好懂的，本人水平较差，如果测试有问题，欢迎回复指出
地址：(function(global) { function isFunction(val) { return typeof val == 'function'; } function isObject(val) { return typeof val == 'object'; } function asyncExcute(fn) { return function() { setTimeout(fn); // 同一执行队列中,原生Promise是先于setTimeout实现的,自己实现暂时用setTimeout模拟 } } function Promise(fn) { if (!isFunction(fn) || this instanceof Promise == false) { throw new TypeError("Promise必须传入function并且new构造") } this.status = 'pending'; this.value = undefined; // promise状态改变之后传递的值 this.thenPromise = undefined; //执行then之后返回的promise this.resolveQueue = []; // this.rejectQueue = []; // var re = asyncExcute(function(resolveData) { this._resolve(resolveData) }.bind(this)), //这里必须异步处理,否则then函数执行以前可能就已经执行了_resolve,但这时then中函数还未加入resolveQueue中 rj = asyncExcute(function(resolveData) { this._reject(resolveData) }.bind(this)); try { fn(re, rj) } catch (error) { this.status = 'reject'; this.value = error; asyncExcute(function(){this._reject(error)}); // new Promise(()=>{ 出现异常... }).then(refn,rjfn); 出现异常时then还未执行, rjfn还未加入到rejectQueue中 } } Promise.prototype.then = function(refn, rjfn) { var returnPro = new Promise(function() {}); this.thenPromise = returnPro; this.resolveQueue.push(refn); this.rejectQueue.push(rjfn); if (this.status == 'resolve') { //执行then时,如果状态已经不是pending,则执行相应函数 this._resolve(this.value); } if (this.status == 'reject') { this._reject(this.value); } return returnPro; } Promise.prototype._resolve = function(resolveData) { var handle, returnVal; this.status = "resolve"; this.value = resolveData; while (this.resolveQueue.length > 0) { //2.2.6 当 promise 成功执行时，所有 onFulfilled 需按照其注册顺序依次回调 handle = this.resolveQueue.shift(); if (!isFunction(handle)) { //不是函数 2.1.1 onFulfilled 不是函数，其必须被忽略 this.thenPromise.value = resolveData; this.thenPromise.status = 'resolve'; this.thenPromise._resolve(); return; } try { //如果 onFulfilled 或者 onRejected 抛出一个异常 e ，则 promise2 必须拒绝执行，并返回拒因 e returnVal = handle(resolveData); } catch (error) { this.thenPromise.status = 'reject'; this.thenPromise.value = error; this.thenPromise._reject(); } if (isObject(returnVal || isFunction(returnVal))) { //如果返回值为对象或者函数 if (returnVal == this.thenPromise) { //如果 promise 和 x 指向同一对象，以 TypeError 为据因拒绝执行 promise this.thenPromise.status = 'reject'; this.thenPromise.value = new TypeError('[[Resolve]](promise, x),promise 和 x 不能指向同一对象'); } else if (returnVal instanceof Promise) { //如果 x 为 Promise ，则使 promise 接受 x 的状态 try { then.call(returnVal, this.thenPromise._resolve.bind(this.thenPromise), this.thenPromise._reject.bind(this.thenPromise)); } catch (error) { this.thenPromise.status = 'reject'; this.thenPromise.value = error; this.thenPromise._reject(); } } else { //如果 x 为对象或者函数 try { //如果取 x.then 的值时抛出错误 e ，则以 e 为据因拒绝 promise var then = returnVal.then; if (isFunction(then)) { then.call(returnVal, this.thenPromise._resolve.bind(this.thenPromise), this.thenPromise._reject.bind(this.thenPromise)); } } catch (error) { this.thenPromise.status = 'reject'; this.thenPromise.value = error; this.thenPromise._reject(); } } } else { this.thenPromise.value = returnVal; this.thenPromise.status = 'resolve'; this.thenPromise._resolve(); } } } Promise.prototype._reject = function(resolveData) { var handle, returnVal; this.status = "resolve"; this.value = resolveData; while (this.rejectQueue.length > 0) { //2.2.6 当 promise 成功执行时，所有 onFulfilled 需按照其注册顺序依次回调 handle = this.rejectQueue.shift(); if (!isFunction(handle)) { //不是函数 2.1.1 onFulfilled 不是函数，其必须被忽略 this.thenPromise.value = resolveData; this.thenPromise.status = 'resolve'; this.thenPromise._resolve(); return; } try { //如果 onFulfilled 或者 onRejected 抛出一个异常 e ，则 promise2 必须拒绝执行，并返回拒因 e returnVal = handle(resolveData); } catch (error) { this.thenPromise.status = 'reject'; this.thenPromise.value = error; this.thenPromise._reject(); } if (isObject(returnVal || isFunction(returnVal))) { //如果返回值为对象或者函数 if (returnVal == this.thenPromise) { //如果 promise 和 x 指向同一对象，以 TypeError 为据因拒绝执行 promise this.thenPromise.status = 'reject'; this.thenPromise.value = new TypeError('[[Resolve]](promise, x),promise 和 x 不能指向同一对象'); } else if (returnVal instanceof Promise) { //如果 x 为 Promise ，则使 promise 接受 x 的状态 try { then.call(returnVal, this.thenPromise._resolve.bind(this.thenPromise), this.thenPromise._reject.bind(this.thenPromise)); } catch (error) { this.thenPromise.status = 'reject'; this.thenPromise.value = error; this.thenPromise._reject(); } } else { //如果 x 为对象或者函数 try { //如果取 x.then 的值时抛出错误 e ，则以 e 为据因拒绝 promise var then = returnVal.then; if (isFunction(then)) { then.call(returnVal, this.thenPromise._resolve.bind(this.thenPromise), this.thenPromise._reject.bind(this.thenPromise)); } } catch (error) { this.thenPromise.status = 'reject'; this.thenPromise.value = error; this.thenPromise._reject(); } } } else { this.thenPromise.value = returnVal; this.thenPromise.status = 'resolve'; this.thenPromise._resolve(); } } } Promise.resolve = function(value) { return new Promise(function(re, rj) { re(value) }) } Promise.reject = function(value) { return new Promise(function(re, rj) { re(value) }) } Promise.all = function(queue) { if (Object.prototype.toString.call(queue) != "[object Array]") { return; } var returnPromise = new Promise(function() {}), resolveNum = 0; for (var i = 0; i < queue.length; i++) { queue[i].then(function() { resolveNum++; if (resolveNum == queue.length) { returnPromise._resolve(); } }); } return returnPromise; } Promise.race = function(queue) { if (Object.prototype.toString.call(queue) != "[object Array]") { return; } var returnPromise = new Promise(function() {}), resolveNum = 0; for (var i = 0; i < queue.length; i++) { queue[i].then(function() { returnPromise._resolve(); }); } return returnPromise; } global.Promise = Promise;})(window);