07-reactive-js.ts

// A library with reactive primitives

import { cooked } from "../../string-cooked.js"

let currentEffect: (() => void) | undefined

export function createEffect(fn: () => void) {
    try {
        var parentEffect = currentEffect
        currentEffect = fn
        fn()
    } finally {
        currentEffect = parentEffect
    }
}

export function createSignal<T>(
    value: T,
): [get: () => T, set: (value: T) => void] {
    const listeners = new Set<() => void>()

    return [
        () => {
            if (currentEffect) {
                listeners.add(currentEffect)
            }

            return value
        },
        (val) => {
            value = val
            listeners.forEach((fn) => fn())
        },
    ]
}

export function createMemo<T>(fn: () => T): () => T {
    const [get, set] = (createSignal as any)() as ReturnType<
        typeof createSignal<T>
    >

    createEffect(() => set(fn()))

    return get
}

export function string(
    strings: readonly string[],
    ...values: readonly unknown[]
) {
    return createMemo(() =>
        cooked(
            strings,
            values.map((value) =>
                typeof value == "function" ? value() : value,
            ),
        ),
    )
}