mini signal implement

mini-signal.ts

let currentListener: Function | undefined = undefined

function createSignal<T>(initialValue: T) {
  let value = initialValue

  const subscribers = new Set<Function>()

  const read = () => {
    if (currentListener !== undefined) {
      subscribers.add(currentListener)
    }

    return value
  }

  const write = (newValue: T) => {
    value = newValue
    subscribers.forEach((fn: Function) => fn())
  }

  return [read, write] as const
}

function createEffect(callback: Function) {
  currentListener = callback
  callback()
  currentListener = undefined
}

const [count, setCount] = createSignal(0)

createEffect(() => {
  console.log(count())
})

setInterval(() => {
  setCount(count() + 2)
}, 1000)

TypeScript version, inspired from SolidJS.

modified from: https://www.lksh.dev/blog/writing-your-own-reactive-signal-library