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atom.ts
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atom.ts
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type Awaited<T> = T extends Promise<infer V> ? Awaited<V> : T
type Getter = {
<Value>(atom: Atom<Value | Promise<Value>>): Value
<Value>(atom: Atom<Promise<Value>>): Value
<Value>(atom: Atom<Value>): Awaited<Value>
}
type WriteGetter = Getter & {
<Value>(
atom: Atom<Value | Promise<Value>>,
options: { unstable_promise: true }
): Promise<Value> | Value
<Value>(atom: Atom<Promise<Value>>, options: { unstable_promise: true }):
| Promise<Value>
| Value
<Value>(atom: Atom<Value>, options: { unstable_promise: true }):
| Promise<Awaited<Value>>
| Awaited<Value>
}
type Setter = {
<Value, Result extends void | Promise<void>>(
atom: WritableAtom<Value, undefined, Result>
): Result
<Value, Update, Result extends void | Promise<void>>(
atom: WritableAtom<Value, Update, Result>,
update: Update
): Result
}
type Read<Value> = (get: Getter) => Value
type Write<Update, Result extends void | Promise<void>> = (
get: WriteGetter,
set: Setter,
update: Update
) => Result
type WithInitialValue<Value> = {
init: Value
}
export type Scope = symbol | string | number
// Not exported for public API
// Are there better typings?
export type SetAtom<
Update,
Result extends void | Promise<void>
> = undefined extends Update
? (update?: Update) => Result
: (update: Update) => Result
type OnUnmount = () => void
type OnMount<Update, Result extends void | Promise<void>> = <
S extends SetAtom<Update, Result>
>(
setAtom: S
) => OnUnmount | void
export type Atom<Value> = {
toString: () => string
debugLabel?: string
read: Read<Value>
}
export type WritableAtom<
Value,
Update,
Result extends void | Promise<void> = void
> = Atom<Value> & {
write: Write<Update, Result>
onMount?: OnMount<Update, Result>
}
type SetStateAction<Value> = Value | ((prev: Value) => Value)
export type PrimitiveAtom<Value> = WritableAtom<Value, SetStateAction<Value>>
let keyCount = 0 // global key count for all atoms
// writable derived atom
export function atom<Value, Update, Result extends void | Promise<void> = void>(
read: Read<Value>,
write: Write<Update, Result>
): WritableAtom<Value, Update, Result>
// read-only derived atom
export function atom<Value>(read: Read<Value>): Atom<Value>
// invalid function in the first argument
export function atom(invalidFunction: (...args: any) => any, write?: any): never
// write-only derived atom
export function atom<Value, Update, Result extends void | Promise<void> = void>(
initialValue: Value,
write: Write<Update, Result>
): WritableAtom<Value, Update, Result> & WithInitialValue<Value>
// primitive atom
export function atom<Value>(
initialValue: Value
): PrimitiveAtom<Value> & WithInitialValue<Value>
export function atom<Value, Update, Result extends void | Promise<void>>(
read: Value | Read<Value>,
write?: Write<Update, Result>
) {
const key = `atom${++keyCount}`
const config = {
toString: () => key,
} as WritableAtom<Value, Update, Result> & { init?: Value }
if (typeof read === 'function') {
config.read = read as Read<Value>
} else {
config.init = read
config.read = (get) => get(config)
config.write = (get, set, update) =>
set(config, typeof update === 'function' ? update(get(config)) : update)
}
if (write) {
config.write = write
}
return config
}