-
Notifications
You must be signed in to change notification settings - Fork 0
/
make-promise-observer.ts
52 lines (44 loc) · 1.21 KB
/
make-promise-observer.ts
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
/* eslint-disable no-void */
import type { AnyPromise } from '@oakfinch/ts-extra'
import { noop } from '../function/noop'
type Callback = <T extends AnyPromise, U extends AnyPromise[]>(promise: T, pending: U) => void
interface PromiseObserver {
observe: <T extends AnyPromise>(promise: T) => T
unobserve: <T extends AnyPromise>(promise: T) => T | undefined
}
export const makePromiseObserver = ({
onBeforeChange = noop,
onChange = noop,
}: {
onBeforeChange?: Callback
onChange?: Callback
}): PromiseObserver => {
const pending = new Set<AnyPromise>()
const observer: PromiseObserver = {
unobserve: promise => {
if (pending.has(promise)) {
onBeforeChange(promise, [...pending])
pending.delete(promise)
onChange(promise, [...pending])
return promise
}
return undefined
},
observe: promise => {
onBeforeChange(promise, [...pending])
pending.add(promise)
onChange(promise, [...pending])
promise.then(
() => {
void observer.unobserve(promise)
},
() => {
void observer.unobserve(promise)
}
)
return promise
},
}
return observer
}
export default makePromiseObserver