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promise.js
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promise.js
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import check from './check.js'
class Promise {
static resolve(value) {
if (value instanceof Promise) return value
return new Promise((resolve, reject) => {
if (value && value.then && typeof value.then === 'function') {
value.then(resolve, reject)
} else {
resolve(value)
}
})
}
static reject(reason) {
if (reason instanceof Promise) return reason
return new Promise((resolve, reject) => {
if (reason && reason.then && typeof reason.then === 'function') {
reason.then(resolve, reject)
} else {
reject(reason)
}
})
}
static all(promises) {
if (!promises || typeof promises[Symbol.iterator] !== 'function') {
throw TypeError(
`${typeof promises} is not iterable (cannot read property Symbol(Symbol.iterator))`,
)
}
let index = 0
const res = []
return new Promise((resolve, reject) => {
const n = promises.length
if (!n) return []
else {
function processPromise(value, i) {
res[i] = value
if (++index === n) resolve(res)
}
for (let i = 0; i < n; i++) {
Promise.resolve(promises[i]).then(
(value) => {
processPromise(value, i)
},
(reason) => {
reject(reason)
},
)
}
}
})
}
static race(promises) {
if (!promises || typeof promises[Symbol.iterator] !== 'function') {
throw TypeError(
`${typeof promises} is not iterable (cannot read property Symbol(Symbol.iterator))`,
)
}
if (!promises.length) {
throw Error('Promise.race need length')
}
return new Promise((resolve, reject) => {
for (const promise of promises) {
Promise.resolve(promise).then(
(value) => {
resolve(value)
},
(reason) => {
reject(reason)
},
)
}
})
}
state = 'pending'
value = null
reason = null
onFulfilledCallback = []
onRejectedCallback = []
constructor(executor) {
if (typeof executor !== 'function') {
throw TypeError('executor is not a function!')
}
this.resolve = this.resolve.bind(this)
this.reject = this.reject.bind(this)
executor(this.resolve, this.reject)
}
resolve(value) {
if (this.state === 'pending') {
this.state = 'fulfilled'
this.value = value
this.onFulfilledCallback.forEach((fn) => {
fn(this.value)
})
}
}
reject(reason) {
if (this.state === 'pending') {
this.state = 'rejected'
this.reason = reason
this.onRejectedCallback.forEach((fn) => {
fn(this.reason)
})
}
}
then(onFulfilled, onRejected) {
if (typeof onFulfilled !== 'function') {
onFulfilled = function (value) {
return value
}
}
if (typeof onRejected !== 'function') {
onRejected = function (reason) {
return reason
}
}
const promise = new Promise((resolve, reject) => {
if (this.state === 'fulfilled') {
try {
const result = onFulfilled(this.value)
check(promise, result, resolve, reject)
} catch (e) {
reject(e)
}
}
if (this.state === 'rejected') {
try {
const result = onRejected(this.reason)
check(promise, result, resolve, reject)
} catch (e) {
reject(e)
}
}
if (this.state === 'pending') {
this.onFulfilledCallback.push((value) => {
try {
const result = onFulfilled(value)
check(promise, result, resolve, reject)
} catch (e) {
reject(e)
}
})
this.onRejectedCallback.push((reason) => {
try {
const result = onRejected(reason)
check(promise, result, resolve, reject)
} catch (e) {
reject(e)
}
})
}
})
return promise
}
finally(callback) {
return this.then(
() => Promise.resolve(callback()),
() => Promise.reject(callback()),
)
}
}
export default Promise