A bowling score calculator

BowlingScoreSimulation.js

// Assuming input is in form of [[1,2], [2,3], [10,0]]
// Came across this problem on the internet
// More at: https://blog.emilmoe.com/bowling-score-simulation/

module.exports = {
  /**
   * Return a list of accumulated result for an input array of scores in different throws
   * @param   Array     attempts the attempts in the game
   * @returns {Array}   Score after each round, cummulatively
   */
  calculateScore: function (attempts) {
    var grandTotal = 0;
    var totalScore = [];

    for(var i=0; i<attempts.length; i++) {
      if (isStrike(attempts[i])) {
        grandTotal += getStrikeScore(attempts, i);
      } else if (isSpare(attempts[i])) {
        grandTotal += getSpareScore(attempts, i);
      } else {
        grandTotal += attempts[i][0] + attempts[i][1];
      }
      totalScore.push(grandTotal);
    }

    return totalScore;
  }
};

function isStrike(attempt) {
  return attempt[0] === 10;
}

function getStrikeScore(attempts, i) {
  var total = 10;                   // initialize with this attempt's score

  if (attempts[i+1] != null) {
    if (isStrike(attempts[i+1])) {
      total += 10;                  // add score of second strike
      if (attempts[i+2] != null) {
        total += attempts[i+2][0];  // add the third attempt's first throw irrespective of it being a strike
      }
    } else {
      total += (attempts[i+1][0] + attempts[i+1][1]);
    }
  }

  return total;
}

function isSpare(attempt) {
  return attempt[0] < 10 && attempt[0] + attempt[1] === 10;
}

function getSpareScore(attempts, i) {
  var total = 10;                   //initialize with spare score

  if (attempts[i+1] != null) {
    total += attempts[i+1][0];
  }

  return total;
}