前端面试题 - 如何实现promise？

• 通过构造函数生成一个promise对象，该构造函数有一个延时函数参数
• 通过promise.then()或promise.catch()方法实现结果获取
• then函数和catch函数可以链式调用

function MyPromise(func) {this.status = 'pending';this.res = '';this.thenCbs = [];this.catchCbs = [];const resolve = (data) => {this.status = 'fulfilled';this.res = data;this.thenCbs.forEach(cb => {cb(this.res);});}const reject = (data) => {this.status = 'rejected';this.res = data;this.catchCbs.forEach(cb => {cb(this.res);});}this.then = function (cb) {if (this.status == 'pending') {this.thenCbs.push(cb);}if (this.status == 'fulfilled') {var res = cb(this.res)}return this;}this.catch = function (cb) {if (this.status == 'pending') {this.catchCbs.push(cb)}if (this.status == 'rejected') {var res = cb(this.res)}return this;}func(resolve, reject)
}

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