Class 版

class mPromise {// 构造器constructor(executor) {// 添加属性this.PromiseState = "pending";this.PromiseResult = null;this.callbacks = [];const _this = this;function resolve(data) {if (_this.PromiseState !== "pending") return;_this.PromiseState = "fulfilled";_this.PromiseResult = data;// 执行 then onResolved 回调函数setTimeout(() => {_this.callbacks.forEach((item) => {item.onResolved(data);});});}function reject(data) {if (_this.PromiseState !== "pending") return;_this.PromiseState = "rejected";_this.PromiseResult = data;// 执行 then onRejected 回调函数setTimeout(() => {_this.callbacks.forEach((item) => {item.onRejected(data);});});}try {executor(resolve, reject);} catch (e) {reject(e);}}// then 方法then(onResolved, onRejected) {const _this = this;// 判断回调函数数组中是否是正确的回调函数// 用于实现 catch 的异常穿透，添加默认的 onRejected 回调函数if (typeof onRejected !== "function") {// 如果不是函数，就创建一个函数，抛出异常onRejected = (err) => {throw err;};}// then 没有指定 onResolved 回调函数，添加默认的 onResolved 回调函数if (typeof onResolved !== "function") {onResolved = (val) => val;}return new mPromise((resolve, reject) => {// 封装回调函数function callback(onResult) {try {const result = onResult(_this.PromiseResult);if (result instanceof mPromise) {result.then((val) => {resolve(val);},(err) => {reject(err);});} else {resolve(result);}} catch (e) {reject(e);}}// 调用回调函数if (this.PromiseState === "fulfilled") {setTimeout(() => {callback(onResolved);});}if (this.PromiseState === "rejected") {setTimeout(() => {callback(onRejected);});}if (this.PromiseState === "pending") {// 保存回调函数// 使用数组保存是为了解决多次调用then方法的问题this.callbacks.push({onResolved: () => {callback(onResolved);},onRejected: () => {callback(onRejected);},});}});}// catch 方法catch(onRejected) {return this.then(undefined, onRejected);}// resolve 方法, 是对象方法，不属于实例对象方法static resolve(value) {return new mPromise((resolve, reject) => {if (value instanceof mPromise) {value.then((val) => {resolve(val);},(err) => {reject(err);});} else {resolve(value);}});}// reject 方法, 是对象方法，不属于实例对象方法static reject(err) {return new mPromise((resolve, reject) => {reject(err);});}// all 方法static all(promises) {return new mPromise((resolve, reject) => {let count = 0;const arr = [];promises.forEach((promise, i) => {promise.then((val) => {arr[i] = val;count++;if (count === promises.length) {resolve(arr);}},(err) => {reject(err);});});});}// race 方法static race(promises) {return new mPromise((resolve, reject) => {promises.forEach((promise) => {promise.then((val) => {resolve(val);},(err) => {reject(err);});});});}
}

function 版

// 声明构造函数
function mPromise(executor) {// 添加属性this.PromiseState = "pending";this.PromiseResult = null;this.callbacks = [];const _this = this;function resolve(data) {if (_this.PromiseState !== "pending") return;_this.PromiseState = "fulfilled";_this.PromiseResult = data;// 执行 then onResolved 回调函数setTimeout(() => {_this.callbacks.forEach((item) => {item.onResolved(data);});});}function reject(data) {if (_this.PromiseState !== "pending") return;_this.PromiseState = "rejected";_this.PromiseResult = data;// 执行 then onRejected 回调函数setTimeout(() => {_this.callbacks.forEach((item) => {item.onRejected(data);});});}try {executor(resolve, reject);} catch (e) {reject(e);}
}mPromise.prototype.then = function (onResolved, onRejected) {const _this = this;// 判断回调函数数组中是否是正确的回调函数// 用于实现 catch 的异常穿透，添加默认的 onRejected 回调函数if (typeof onRejected !== "function") {// 如果不是函数，就创建一个函数，抛出异常onRejected = (err) => {throw err;};}// then 没有指定 onResolved 回调函数，添加默认的 onResolved 回调函数if (typeof onResolved !== "function") {onResolved = (val) => val;}return new mPromise((resolve, reject) => {// 封装回调函数function callback(onResult) {try {const result = onResult(_this.PromiseResult);if (result instanceof mPromise) {result.then((val) => {resolve(val);},(err) => {reject(err);});} else {resolve(result);}} catch (e) {reject(e);}}// 调用回调函数if (this.PromiseState === "fulfilled") {setTimeout(() => {callback(onResolved);});}if (this.PromiseState === "rejected") {setTimeout(() => {callback(onRejected);});}if (this.PromiseState === "pending") {// 保存回调函数// 使用数组保存是为了解决多次调用then方法的问题this.callbacks.push({onResolved: () => {callback(onResolved);},onRejected: () => {callback(onRejected);},});}});
};mPromise.prototype.catch = function (onRejected) {return this.then(undefined, onRejected);
};// 注意：这里是函数对象方法，不是实例对象方法
mPromise.resolve = function (value) {return new mPromise((resolve, reject) => {if (value instanceof mPromise) {value.then((val) => {resolve(val);},(err) => {reject(err);});} else {resolve(value);}});
};mPromise.reject = function (err) {return new mPromise((resolve, reject) => {reject(err);});
};mPromise.all = function (promises) {return new mPromise((resolve, reject) => {let count = 0;const arr = [];promises.forEach((promise, i) => {promise.then((val) => {arr[i] = val;count++;if (count === promises.length) {resolve(arr);}},(err) => {reject(err);});});});
};mPromise.race = function (promises) {return new mPromise((resolve, reject) => {promises.forEach((promise) => {promise.then((val) => {resolve(val);},(err) => {reject(err);});});});
};