Rock, paper and scissors. Memoizer solution

rps.js

const memoizer = (fn, initialState = null) => {
  const _cache = initialState || {}

  return (...params) => {
    const _stringified = JSON.stringify(params)

    if (_cache[_stringified] === undefined) {
      const result = fn(...params)
      _cache[_stringified] = result

      return result
    }

    return _cache[_stringified]
  }
}

const getWinner = memoizer((p1, p2) => {
  const getSignal = (p1, p2) => {
    const signals = ['rock', 'paper', 'scissors']
    const index = (signals.indexOf(p1) + signals.indexOf(p2)) - 1

    return ['paper', 'rock', 'scissors'][index]
  }
  
  return [p1, p2].indexOf(getSignal(p1, p2)) + 1
})

const rps = (p1, p2) => {
  if (p1 === p2) {
    return 'Draw!'
  }

  return `Player ${getWinner(p1, p2)} won!`
}