//promise：then,catch,finally,all,race
// then时state还是pending等待状态 我们就需要在then调用的时候，将成功和失败存到各自的数组，一旦reject或者resolve，就调用它们，类似发布订阅
//pending,fulfilled,rejected
const pedding = 'pedding'
const fulfilled = 'fulfilled'
const rejected = 'rejected'
class Promise {
constructor(executor) {
console.log('executor:'+ executor)
this.status = pedding //初始状态
this.value = undefined //成功或者失败的值
this.fail = undefined
this.successCallback = [] //成功或者失败的回调函数
this.errorCallback = []
let resolve = (value) => { //成功之后就依次执行
setTimeout(() => {
if (this.status === pedding) {//只有在状态是pending的时候才能改变
//console.log('resolve:'+value)
this.status = fulfilled
this.value = value
this.successCallback.forEach(fn => {
fn()
})
}
}, 0);
};
let reject = (fail) => {
setTimeout(() => {
if (this.status === pedding) {
// console.log('reject：'+ fail)
this.status = rejected
this.fail = fail
this.errorCallback.forEach(fn => {
fn()
})
}
}, 0);
};
try {
executor(resolve,reject)
}catch(err){
reject(err)
}
}
then(success,error) {
if(this.status === fulfilled) {
return new Promise((resolve,reject) => {
try{
let fun = success(this.value)
if(fun instanceof Promise) {
fun.then(resolve,reject)
}else{
resolve(fun)
}
}catch(err) {
reject(err)
}
})
}
if(this.status === rejected) {
return new Promise((resolve, reject) => {
try {
let j = error(this.fail)
if (j instanceof Promise) {
j.then(resolve, reject)
} else {
resolve(j)
}
} catch (err) {
reject(err)
}
})
}
// console.log(this.reject)
// 订阅成功失败
if(this.status === pedding) {//刚进来必须是pedding状态，否则状态一旦变了回调还没有注册
return new Promise((resolve, reject) => {
this.successCallback.push(() => {
let f = success(this.value)
if (f instanceof Promise) {
f.then(resolve, reject)
} else {
resolve(f)
}
})
this.errorCallback.push(() =>{
let j = error(this.fail)
if (j instanceof Promise) {
j.then(resolve, reject)
} else {
resolve(j)
}
})
})
}
}
}
let p = new Promise((resolve,reject) =>{
//reject('失败')
resolve('成功1')
})
p.then((res) => {
console.log('then的第一个参数成功'+res)
return new Promise((resolve,reject) =>{
//reject('失败')
resolve('成功2')
})
},()=>{
console.log('失败')
}).then((res) => {
console.log('then的第二个参数成功'+res)
},()=>{
console.log('失败2')
})
// .then((res) => {
// console.log('then的第3个参数成功'+res)
// },()=>{
// console.log('失败3')
// })
// p.then()
//直接在then后面then 报错Cannot read property 'then' of undefined，所以需要返回一个新的promise对象
输出
executor:(resolve,reject) =>{
//reject('失败')
resolve('成功1')
}
executor:(resolve, reject) => {
this.successCallback.push(() => {
let f = success(this.value)
if (f instanceof Promise) {
f.then(resolve, reject)
} else {
resolve(f)
}
})
this.errorCallback.push(() =>{
let j = error(this.fail)
if (j instanceof Promise) {
j.then(resolve, reject)
} else {
resolve(j)
}
})
}
executor:(resolve, reject) => {
this.successCallback.push(() => {
let f = success(this.value)
if (f instanceof Promise) {
f.then(resolve, reject)
} else {
resolve(f)
}
})
this.errorCallback.push(() =>{
let j = error(this.fail)
if (j instanceof Promise) {
j.then(resolve, reject)
} else {
resolve(j)
}
})
}
then的第一个参数成功成功1
executor:(resolve,reject) =>{
//reject('失败')
resolve('成功2')
}
executor:(resolve, reject) => {
this.successCallback.push(() => {
let f = success(this.value)
if (f instanceof Promise) {
f.then(resolve, reject)
} else {
resolve(f)
}
})
this.errorCallback.push(() =>{
let j = error(this.fail)
if (j instanceof Promise) {
j.then(resolve, reject)
} else {
resolve(j)
}
})
}
then的第二个参数成功成功2
[Done] exited with code=0 in 0.095 seconds
