- 創(chuàng)建一個 Promise.js 文件
function Promise(executor) { // executor是一個執(zhí)行函數(shù)
let self = this;
self.status = 'pending';
self.value = undefined; // 默認(rèn)成功的值
self.reason = undefined; // 默認(rèn)失敗的原因
self.onResolvedCallbacks = []; // 存放then成功的回調(diào)
self.onRejectedCallbacks = []; // 存放then失敗的回調(diào)
function resolve(value) { // 成功狀態(tài)
if (self.status === 'pending') {
self.status = 'resolved';
self.value = value;
self.onResolvedCallbacks.forEach(function (fn) {
fn();
});
}
}
function reject(reason) { // 失敗狀態(tài)
if (self.status === 'pending') {
self.status = 'rejected';
self.reason = reason;
self.onRejectedCallbacks.forEach(function (fn) {
fn();
})
}
}
try {
executor(resolve, reject)
} catch (e) { // 捕獲的時候發(fā)生異常,就直接失敗了
reject(e);
}
}
function resolvePromise(promise2, x, resolve, reject) {
// 有可能這里返回的x是別人的promise
// 盡可能允許其他亂寫
if (promise2 === x) { //這里應(yīng)該報一個類型錯誤，有問題
return reject(new TypeError('循環(huán)引用了'))
}
// 看x是不是一個promise,promise應(yīng)該是一個對象
let called; // 表示是否調(diào)用過成功或者失敗
if (x !== null && (typeof x === 'object' || typeof x === 'function')) {
// 可能是promise {},看這個對象中是否有then方法，如果有then我就認(rèn)為他是promise了
try { // {then:1}
let then = x.then;
if (typeof then === 'function') {
// 成功
then.call(x, function (y) {
if (called) return
called = true
// y可能還是一個promise，在去解析直到返回的是一個普通值
resolvePromise(promise2, y, resolve, reject)
}, function (err) { //失敗
if (called) return
called = true
reject(err);
})
} else {
resolve(x)
}
} catch (e) {
if (called) return
called = true;
reject(e);
}
} else { // 說明是一個普通值1
resolve(x); // 表示成功了
}
}
Promise.prototype.then = function (onFulfilled, onRjected) {
//成功和失敗默認(rèn)不穿給一個函數(shù)
onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : function (value) {
return value;
}
onRjected = typeof onRjected === 'function' ? onRjected : function (err) {
throw err;
}
let self = this;
let promise2; //返回的promise
if (self.status === 'resolved') {
promise2 = new Promise(function (resolve, reject) {
// 當(dāng)成功或者失敗執(zhí)行時有異常那么返回的promise應(yīng)該處于失敗狀態(tài)
// x可能是一個promise 也有可能是一個普通的值
setTimeout(function () {
try {
let x = onFulfilled(self.value);
// x可能是別人promise，寫一個方法統(tǒng)一處理
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
})
})
}
if (self.status === 'rejected') {
promise2 = new Promise(function (resolve, reject) {
setTimeout(function () {
try {
let x = onRjected(self.reason);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
})
})
}
// 當(dāng)調(diào)用then時可能沒成功 也沒失敗
if (self.status === 'pending') {
promise2 = new Promise(function (resolve, reject) {
// 此時沒有resolve 也沒有reject
self.onResolvedCallbacks.push(function () {
setTimeout(function () {
try {
let x = onFulfilled(self.value);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e)
}
})
});
self.onRejectedCallbacks.push(function () {
setTimeout(function () {
try {
let x = onRjected(self.reason);
resolvePromise(promise2, x, resolve, reject);
} catch (e) {
reject(e);
}
})
});
})
}
return promise2;
}
// 捕獲錯誤的方法
Promise.prototype.catch = function (callback) {
return this.then(null, callback)
}
// 解析全部方法
// let arr = [];
// arr[1] = 100;
// console.log(arr.length)
Promise.all = function (promises) {
//promises是一個promise的數(shù)組
return new Promise(function (resolve, reject) {
let arr = []; //arr是最終返回值的結(jié)果
let i = 0; // 表示成功了多少次
function processData(index, y) {
arr[index] = y;
if (++i === promises.length) {
resolve(arr);
}
}
for (let i = 0; i < promises.length; i++) {
promises[i].then(function (y) {
processData(i, y)
}, reject)
}
})
}
// 只要有一個promise成功了 就算成功。如果第一個失敗了就失敗了
Promise.race = function (promises) {
return new Promise(function (resolve, reject) {
for (var i = 0; i < promises.length; i++) {
promises[i].then(resolve,reject)
}
})
}
// 生成一個成功的promise
Promise.resolve = function(value){
return new Promise(function(resolve,reject){
resolve(value);
})
}
// 生成一個失敗的promise
Promise.reject = function(reason){
return new Promise(function(resolve,reject){
reject(reason);
})
}
Promise.defer = Promise.deferred = function () {
let dfd = {};
dfd.promise = new Promise(function (resolve, reject) {
dfd.resolve = resolve;
dfd.reject = reject;
});
return dfd
}
module.exports = Promise;
- 其他文件中引入
let Promise = require('./Promise')
// 同步調(diào)用的
let p = new Promise(function(resolve, reject){
// 如果兩個都調(diào)用，誰在前，就調(diào)誰。
reject(100);
resolve(1);
})
// then 接受兩個回調(diào)函數(shù)，一個是成功的回調(diào)，一個是失敗的回調(diào)
p.then(function(data){
console.log('data', data)
},function(err){
console.log('err', err)
})
