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const STATE = {
pending: 'pending',
fulfilled: 'fulfilled',
rejected: 'rejected'
}
class MyPromise {
constructor(executor) {
this.state = STATE.pending
this.value = ''
this.reason = ''
this.onResolveCallbacks = []
this.onRejectedCallbacks = []
let resolve = (value) => {
if (this.state === STATE.pending) {
this.state = STATE.fulfilled
this.value = value
this.onResolveCallbacks.forEach(fn => fn())
}
}
let reject = (reason) => {
if (this.state === STATE.pending) {
this.state = STATE.rejected
this.reason = reason
this.onRejectedCallbacks.forEach(fn => fn())
}
}
try {
executor(resolve, reject)
} catch (err) {
reject(err)
}
}
then(onFulfilled, onRejected) {
onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : value => value
onRejected = typeof onRejected === 'function' ? onRejected : err => {throw err}
let promise2 = new MyPromise((resolve, reject) => {
if (this.state === STATE.fulfilled) {
setTimeout(() => {
try {
let x = onFulfilled(this.value)
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
}
if (this.state === STATE.rejected) {
setTimeout(() => {
try {
let x = onRejected(this.reason)
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
}
if (this.state === STATE.pending) {
this.onResolveCallbacks.push(() => {
setTimeout(() => {
try {
let x = onFulfilled(this.value)
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
})
this.onRejectedCallbacks.push(() => {
setTimeout(() => {
try {
let x = onRejected(this.reason)
resolvePromise(promise2, x, resolve, reject)
} catch (e) {
reject(e)
}
}, 0)
})
}
})
return promise2
}
}
function resolvePromise(promise2, x, resolve, reject) {
if (x === promise2) {
return reject(new TypeError('Chaining cycle detected for promise'))
}
let called
if (x !== null && (typeof x === 'object' || typeof x === 'function')) {
try {
let then = x.then
if (typeof then === 'function') {
then.call(x, y => {
if (called) return;
called = true
resolvePromise(promise2, y, resolve, reject)
}, err => {
if (called) return
called = true
reject(err)
})
} else {
resolve(x)
}
} catch(e) {
if (called) return;
called = true
reject(e)
}
} else {
resolve(x)
}
}
MyPromise.resolve = function (res) {
return new MyPromise((resolve, reject) => {
resolve(res)
})
}
MyPromise.reject = function (err) {
return new MyPromise((resolve, reject) => {
reject(err)
})
}
MyPromise.race = function (promises) {
return new MyPromise((resolve, reject) => {
for (let i = 0, len = promises.length; i < len; i++) {
promises[i].then(resolve, reject)
}
})
}
MyPromise.all = function (promises) {
let arr = []
let index = 0
return new MyPromise((resolve, reject) => {
for (let i = 0, len = promises.length; i < len; i++) {
promises[i].then(res => {
arr.push(res)
index ++
if (index === len) {
resolve(arr)
}
}, err => {
reject(err)
})
}
})
}
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