Promise 是异步的一种解决方案，有reject、resolve、then、catch、all、finally等方法。网上有很多关于Promise的优秀文章，深入浅出，多看看它们的原理和使用会茅塞顿开，但是最重要的还是自己动手敲，即使你只实现一部分，剩下的就能举一反三。
类的方式实现
class CPromise {
constructor(exector) {
this.status = 'pending'// 初始状态为pending
this.value = null// 成功的值
this.reason = null// 失败的原因
this.onFulfilledCallbacks = []//成功的回调函数数组
this.onRejectdCallbacks = []//失败的回调函数数组
let resolve = value => {
if(this.status === 'pending'){
this.status = 'fulfilled'
this.value = value
this.onFulfilledCallbacks.forEach(fn => fn())//调用成功的回调函数
}
}
let reject = reason => {
if(this.status === 'pending'){
this.status = 'reject'
this.reason = reason
this.onRejectdCallbacks.forEach(fn => fn())//调用失败的回调函数
}
}
try{
exector(resolve, reject)
}catch(error) {
reject(error)
}
}
then(onFulfilled, onRejected){
return new CPromise((resolve, reject) => {
if(this.status === 'fulfilled') {
setTimeout(() => {
const x = onFulfilled(this.value)
x instanceof CPromise ? x.then(resolve, reject) : resolve(x)
})
}
if(this.status === 'reject') {
setTimeout(() => {
const x = onRejected(this.reason)
x instanceof CPromise ? x.then(resolve, reject) : resolve(x)
})
}
if(this.status === 'pending') {
this.onFulfilledCallbacks.push(() => {// 将成功的回调放入成功数组
setTimeout(() => {
const x = onFulfilled(this.value)
x instanceof CPromise ? x.then(resolve, reject) : resolve(x)
})
})
this.onRejectedCallbacks.push(() => { //将失败的回调函数放入失败数组
setTimeout(() => {
const x = onRejected(this.reason)
x instanceof CPromise ? x.then(resolve, reject) : resolve(x)
})
})
}
})
}
}
构造函数方式实现
标签：status,resolve,实现,CPromise,value,reason,Promise,reject From： https://www.cnblogs.com/rain111/p/17215028.html未完待续。。。