let promise = new Promise()
let fs = require('mz/fs');　　　　//使用了一个mz的包  mz封装了fs对应的函数，并改为Promise
promise.race([fs.readFile('./name.txt', 'utf8'), fs.readFile('./age.txt', 'utf8')]).then((data) => {console.log(data);
}, err => {console.log(err);
});

function Promise(executor) {let self = this;self.status = 'pending';　　//promise默认就是等待状态self.value = undefined;　　 //存放成功回调的值self.reason = undefined;　　//存放失败回调的值self.onResolved = [];　　//专门存放成功的回调函数self.onRejected = [];　　//存放失败的回调函数
function resolve(value) {　　//promise成功走这个函数if (self.status === 'pending') {self.value = value;self.status = 'resolved';self.onResolved.forEach(fn => fn());}}function reject(reason) {　　//promise失败走这个函数if (self.status === 'pending') {self.reason = reason;self.status = 'rejected';self.onRejected.forEach(fn => fn());}}try {executor(resolve, reject);} catch (e) {reject(e);}
}
//确定then里面的成功/失败函数执行的结果和返回的promise2是什么关系
//ps:promise a+里面确实有很多的槽点  比如这个x、y和promise2什么的都是那里面规定的
function resolvePromise(promise2, x, resolve, reject) {if (promise2 === x) {return reject(new TypeError('循环引用'));}let called;if (x != null && (typeof x === 'object' || typeof x === 'function')) {try {let then = x.then; // 如何判断是promise 就判断又没then方法 if (typeof then === 'function') {then.call(x, (y) => {if (called) return;called = true;resolvePromise(promise2, y, resolve, reject);}, (e) => {if (called) return;called = true;reject(e);});} else {resolve(x);}} catch (e) {if (called) return;called = true;reject(e);}} else {resolve(x);}
}//promise的then方法
Promise.prototype.then = function (onfulfilled, onrejected) {onfulfilled = typeof onfulfilled == 'function' ? onfulfilled : val => val;onrejected = typeof onrejected === 'function' ? onrejected : err => {throw err;}let self = this;let promise2;　　//返回新的promise就是promise2  不要问我为什么 a+里面规范的promise2 = new Promise((resolve, reject) => {if (self.status === 'resolved') {setTimeout(() => { // 目的是为了实现异步try {let x = onfulfilled(self.value);resolvePromise(promise2, x, resolve, reject);} catch (e) {reject(e);}}, 0);}if (self.status === 'rejected') {setTimeout(() => {try {let x = onrejected(self.reason);resolvePromise(promise2, x, resolve, reject); // 解析x 和 promise2的关系} catch (e) {reject(e);}}, 0);}if (self.status === 'pending') {self.onResolved.push(function () {setTimeout(() => {try {let x = onfulfilled(self.value);resolvePromise(promise2, x, resolve, reject);} catch (e) {reject(e);}}, 0);});self.onRejected.push(function () {setTimeout(() => {try {let x = onrejected(self.reason);resolvePromise(promise2, x, resolve, reject);} catch (e) {reject(e);}}, 0);});}})return promise2;
}//实现promise原生方法
Promise.all = function (promises) {return new Promise((resolve, reject) => {let results = []; 　　 let i = 0;function processData(index, data) {results[index] = data; // let arr = []  arr[2] = 100if (++i === promises.length) {resolve(results);}}for (let i = 0; i < promises.length; i++) {let p = promises[i];p.then((data) => { // 成功后把结果和当前索引 关联起来
        processData(i, data);}, reject);}})
}
Promise.race = function (promises) {return new Promise((resolve, reject) => {for (let i = 0; i < promises.length; i++) {let p = promises[i];p.then(resolve, reject);}})
}
Promise.prototype.catch = function (onrejected) {return this.then(null, onrejected)
}
Promise.reject = function (reason) {return new Promise((resolve, reject) => {reject(reason)})
}
Promise.resolve = function (value) {return new Promise((resolve, reject) => {resolve(value);})
}

　// 测试代码是否符合a+ 规范 为了让其能测试
　// npm install promises-aplus-tests -g
　// promises-aplus-tests 文件名 可以测试

Promise.defer = Promise.deferred = function () {let dfd = {};dfd.promise = new Promise((resolve, reject) => {dfd.resolve = resolve;dfd.reject = reject;});return dfd;
}
module.exports = Promise