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tuhongweituhongwei
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增加promise实现
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2 files changed

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‎promise.html‎

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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>promise</title>
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<script src="promise.js"></script>
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</head>
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<body>
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</body>
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</html>

‎promise.js‎

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/**
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* promise实现
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*/
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const isFunction = (val) => {
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return typeof val === 'function';
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};
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function Promise (Fn) {
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// 初始为'PENDING'状态
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this.status = 'PENDING';
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this.value;
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this.reason;
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// 存储onFulfilled
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this.resolves = [];
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// 存储onRejected
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this.rejects = [];
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// let resolve = (value) => {
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// if (this.status === 'PENDING') {
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// // 加上异步处理，保证then方法先执行
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// setTimeout(() => {
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// //状态转换为FULFILLED
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// //执行then时保存到resolves里的回调
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// //如果回调有返回值，更新当前value
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// this.status = 'FULFILLED';
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// this.resolves.forEach(fn => {
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// value = fn(value) || value;
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// });
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// this.value = value;
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// });
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// }
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// }
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// let reject = (reason) => {
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// if (this.status === 'PENDING') {
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// // 加上异步处理，保证reject方法先执行
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// setTimeout(() => {
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// //状态转换为REJECTED
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// //执行then时保存到rejects里的回调
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// //如果回调有返回值，更新当前reason
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// this.status = 'REJECTED';
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// this.rejects.forEach(fn => {
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// reason = fn(reason) || reason;
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// });
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// this.reason = reason;
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// });
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// }
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// }
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let transition = (status, val) => {
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if (this.status === 'PENDING') {
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// 加上异步处理，保证方法先执行
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setTimeout(() => {
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//状态转换为REJECTED
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//执行then时保存到rejects里的回调
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//如果回调有返回值，更新当前reason
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this.status = status;
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let f = status === 'FULFILLED',
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queue = this[f ? 'resolves' : 'rejects'];
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queue.forEach(fn => {
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val = fn(val) || val;
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});
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this[f ? 'value' : 'reason'] = val;
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});
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}
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}
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let resolve = (val) => {
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transition('FULFILLED', val);
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}
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let reject = (reason) => {
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transition('REJECTED', reason);
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}
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try {
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Fn(resolve, reject);
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} catch (err) {
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reject(err);
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}
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}
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Promise.prototype.then = (onFulfilled, onRejected) => {
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if (this.status === 'PENDING') {
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isFunction(onFulfilled) && this.resolves.push(onFulfilled);
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isFunction(onRejected) && this.rejects.push(onRejected);
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} else if (this.status === 'FULFILLED'){
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isFunction(onFulfilled) && onFulfilled(this.value);
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} else if (this.status === 'REJECTED'){
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isFunction(onRejected) && onRejected(this.reason);
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}
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return this;
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}
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Promise.prototype.catch = (onRejected) => {
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return this.then(null, onRejected);
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}
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let getInfo = new Promise((resolve, reject) => {
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resolve('success');
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}).then(r => {
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console.log(r);
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return r + '1';
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}).then(r => {
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console.log(r);
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return r + '2';
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});
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setTimeout(() => {
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getInfo.then(r => {
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console.log(r);
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return r + '3';
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});
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});

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