1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
| const isFunction = obj => typeof obj === 'function'
, isObject = obj => !!(obj && typeof obj === 'object')
, isThenable = obj => (isFunction(obj) || isObject(obj)) && 'then' in obj
, isPromise = promise => promise instanceof Promise
, nextTick = queueMicrotask || setTimeout
const PENDING = 'pending', FULFILLED = 'fulfilled', REJECTED = 'rejected'
class Promise {
result = null
state = PENDING
callbacks = []
constructor(fn) {
let onFulfilled = value => this.#transition(FULFILLED, value)
let onRejected = reason => this.#transition(REJECTED, reason)
let ignore = false
let resolve = value => ignore || (ignore = true, this.#resolvePromise(value, onFulfilled, onRejected))
let reject = reason => ignore || (ignore = true, onRejected(reason))
try {
fn(resolve, reject)
} catch (error) {
reject(error)
}
}
then(onFulfilled, onRejected) {
return new Promise((resolve, reject) => {
let callback = { onFulfilled, onRejected, resolve, reject }
if (this.state === PENDING) this.callbacks.push(callback)
else nextTick(() => handleCallback(callback, this.state, this.result))
})
}
#transition(state, result) {
this.state = state, this.result = result
nextTick(() => (this.callbacks.map(e => handleCallback(e, state, result)), this.callbacks.length = 0))
}
#resolvePromise(result, resolve, reject) {
if (result === this) return reject(new TypeError('Can not fufill promise with itself'))
if (isPromise(result)) return result.then(resolve, reject)
if (isThenable(result)) {
try {
let then = result.then
if (isFunction(then)) return new Promise(then.bind(result)).then(resolve, reject)
} catch (error) {
return reject(error)
}
}
resolve(result)
}
}
const handleCallback = (callback, state, result) => {
let { onFulfilled, onRejected, resolve, reject } = callback
try {
if (state === FULFILLED)
isFunction(onFulfilled) ? resolve(onFulfilled(result)) : resolve(result)
if (state === REJECTED)
isFunction(onRejected) ? resolve(onRejected(result)) : reject(result)
} catch (error) {
reject(error)
}
}
Promise.prototype.catch = function (onRejected) {
return this.then(null, onRejected)
}
Promise.resolve = value => new Promise(resolve => resolve(value))
Promise.reject = reason => new Promise((_, reject) => reject(reason))
const resolved = value => new Promise(resolve => resolve(value))
const rejected = reason => new Promise((_, reject) => reject(reason))
const deferred = () => {
let promise, resolve, reject
promise = new Promise(($resolve, $reject) => {
resolve = $resolve
reject = $reject
})
return { promise, resolve, reject }
}
module.exports = { resolved, rejected, deferred }
|
