function once(fn) {
  let hasBeenCalled = false
  let cachedResult;

  return function (...args) {
    if (hasBeenCalled) return cachedResult;

    hasBeenCalled = true
    cachedResult = fn(...args)

    return cachedResult;
  }
}

const addByFiveOnce = once(num => num + 5)

console.log(addByFiveOnce(2))
console.log(addByFiveOnce(9))
console.log(addByFiveOnce(6))