手写Promise
首先,要手写Promise,那必须先了解它的功能和自己打算用的方法。这里推荐先阅读阮一峰的《Promise 对象》以及《Class 的基本语法》
先上代码(待补充异步),这部分已实现resolve、reject、then、catch等功能
class MyPromise { static PENDING = 'pending' static FULFILLED = 'fulfilled' static REJECTED = 'rejected' constructor(func) { this.PromiseState = MyPromise.PENDING this.PromiseResult = null try { func(this.resolve.bind(this), this.reject.bind(this)) } catch (error) { this.reject(error) } } resolve(result) { if (this.PromiseState === MyPromise.PENDING) { this.PromiseState = MyPromise.FULFILLED this.PromiseResult = result } } reject(reason) { if (this.PromiseState === MyPromise.PENDING) { this.PromiseState = MyPromise.REJECTED this.PromiseResult = reason } } then(onFulfilled, onRejected) { onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : value => value onRejected = typeof onRejected === 'function' ? onRejected : reason => { throw reason } if (this.PromiseState === MyPromise.FULFILLED) { onFulfilled(this.PromiseResult) } if (this.PromiseState === MyPromise.REJECTED) { onRejected(this.PromiseResult) } } } let promise1 = new MyPromise((resolve, reject) => { resolve('success') }) promise1.then(result => { console.log('result:', result) }, reason => { console.log('reason:', reason ) }) console.log(promise1)