03-tiny-store.ts

// A simple signal, effect, memo, and computed library based on SolidJS.

let currentScope: () => void

export function createEffect(update: () => void) {
    const parent = currentScope
    currentScope = update
    update()
    currentScope = parent
}

export function createSignal<T>(): [() => T | undefined, (value: T) => void]
export function createSignal<T>(value: T): [() => T, (value: T) => void]
export function createSignal<T>(
    value?: T,
): [() => T | undefined, (value: T) => void] {
    const tracking = new Set<() => void>()

    const get = () => {
        if (currentScope) {
            tracking.add(currentScope)
        }

        return value
    }

    const set = (val: T) => {
        value = val
        tracking.forEach((effect) => effect())
    }

    return [get, set]
}

export function createMemo<T>(compute: () => T) {
    const [get, set] = createSignal<T>()
    createEffect(() => set(compute()))
    return get as () => T
}

export function createComputed<T>(value: T, compute: (oldValue: T) => T) {
    const [get, set] = createSignal()
    createEffect(() => set((value = compute(value))))
    return get as () => T
}