/*
1. Promise是一个类，在执行这个类的时候，需要传递一个执行器进去，执行器会立即执行
2. Promise中由三种状态，分别为成功 fulfilled 失败 rejected 等待 pending
pending --> fulfilled
pending --> rejected
一旦状态确定就不可更改
3. resolve和reject是用来更改状态的
resolve：fulfilled
reject： rejected
4. then方法内部做的事情就判断状态，如果状态是成功，调用成功的回调函数，如果状态是失败，调用失败的回调函数。then方法是被定义在原型对象中的
5. then成功回调由一个参数，表示成功之后的值，then失败回调有一个参数，表示失败之后的原因
6. 同一个promise对象下面的then方法是可以被调用多次的
7. then方法是可以被链式调用的, 后面then方法的回调函数拿到值的是上一个then方法的回调函数的返回值
*/
const PENDING = 'pending' //等待
const FULFILLED = 'fulfilled' //成功
const REJECTED = 'rejected'//失败
class MyPromise {
constructor(executor) {
try {
executor(this.resolve, this.reject)
} catch (e) {
this.reject(e)
}
}
// promise 状态
status = PENDING;
// 成功之后的值
value = undefined;
// 失败之后的原因
reason = undefined;
// 成功回调
successCallback = [];
// 失败回调
failCallback = [];
resolve = value => {
// 如果状态不是等待，阻止程序向下执行
if (this.status !== PENDING) return
// 将状态更改为成功
this.status = FULFILLED;
// 保存成功之后的值
this.value = value;
// 判断成功回调是否存在，如果存在则调用
// this.successCallback && this.successCallback(this.value)
while (this.successCallback.length) this.successCallback.shift()()
}
reject = reason => {
// 如果状态不是等待，阻止程序向下执行
if (this.status !== PENDING) return
// 将状态更改为失败
this.status = REJECTED;
// 保存失败之后的原因
this.reason = reason;
// 判断成功回调是否存在，如果存在则调用
// this.failCallback && this.failCallback(this.reason)
while (this.failCallback.length) this.failCallback.shift()()
}
then(successCallback, failCallback) {
successCallback = successCallback ? successCallback : value => value
failCallback = failCallback ? failCallback : reason => { throw reason }
let promise2 = new MyPromise((resolve, reject) => {
// 判断状态
if (this.status === FULFILLED) {
setTimeout(() => {
try {
let x = successCallback(this.value)
// 判断x 的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是调用reject
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
} else if (this.status === REJECTED) {
setTimeout(() => {
try {
let x = failCallback(this.reason)
// 判断x 的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是调用reject
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
} else {
// 等待
// 将成功回调和失败回调存储起来
this.successCallback.push(() => {
setTimeout(() => {
try {
let x = successCallback(this.value)
// 判断x 的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是调用reject
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
})
this.failCallback.push(() => {
setTimeout(() => {
try {
let x = failCallback(this.reason)
// 判断x 的值是普通值还是promise对象
// 如果是普通值，直接调用resolve
// 如果是promise对象，查看promise对象返回的结果
// 再根据promise对象返回的结果，决定调用resolve还是调用reject
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
})
}
})
return promise2
}
catch(failCallback) {
return this.then(undefined, failCallback)
}
finally(callback) {
return this.then((val) => {
return MyPromise.resolve(callback()).then(() => val)
}, reason => {
return MyPromise.resolve(callback()).then(() => { throw reason })
})
}
static all(array) {
let result = [];
let index = 0;
return new MyPromise((resolve, reject) => {
function addData(key, value) {
result[key] = value
index++
if (index === array.length) {
resolve(result)
}
}
for (let i = 0; i < array.length; i++) {
let current = array[i]
if (current instanceof MyPromise) {
// promise对象
current.then(val => addData(i, val), reason => reject(reason))
} else {
// 普通值
addData(i, array[i])
}
}
})
}
static race(array) {
return new MyPromise((resolve, reject) => {
for (let i = 0; i < array.length; i++) {
let current = array[i]
if (current instanceof MyPromise) {
// promise对象
current.then(val => resolve(val), reason => reject(reason))
} else {
// 普通值
resolve(current)
}
}
})
}
static any(array) {
let result = [];
let index = 0;
return new MyPromise((resolve, reject) => {
function addError(key, reason) {
result[key] = reason
index++
if (index === array.length) {
reject(result)
}
}
for (let i = 0; i < array.length; i++) {
let current = array[i]
if (current instanceof MyPromise) {
// promise对象
current.then(val => resolve(val), reason => addError(i, reason))
} else {
// 普通值
resolve(array[i])
}
}
})
}
static resolve(value) {
if (value instanceof MyPromise) return value
return new MyPromise(resolve => resolve(value))
}
static reject(value) {
return new MyPromise((resolve, reject) => reject(value))
}
}
function resolvePromise(promise2, x, resolve, reject) {
if (promise2 === x) {
return reject(new TypeError('Chaining cycle detected for promise #<Promise>'))
}
if (x instanceof MyPromise) {
// promise对象
// x.then(value => resolve(value), reason => reject(reason))
x.then(resolve, reject)
} else {
// 普通值
resolve(x)
}
}
module.exports = MyPromise
