throttle.ts

throttle.ts

export const throttle = <FN extends (...args: Parameters<FN>) => ReturnType<FN>>(
  fn: FN,
  delay: number
) => {
  let wait = false
  let timeout: undefined | number
  let prevValue: ReturnType<FN> | undefined = undefined

  const throttleFn = (...args: Parameters<FN>) => {
    if (wait) {
      // prevValue always defined by the
      // time wait is true
      return prevValue!
    }

    const val = fn(...args)
    prevValue = val

    wait = true

    timeout = window.setTimeout(() => {
      wait = false
    }, delay)

    return val
  }
  throttleFn.cancel = () => {
    clearTimeout(timeout)
  }
  return throttleFn
}