Bowling score string calculation

calculateScore.js

// Darek's `functional` bowling score algorithm!

function calculateScore(str) {
  const rolls = str.split('');
  return rolls.reduce((data, roll, index) => {
    let rollScore = calcRoll(roll, data.prevRoll);
    if (rolls.length - index > 2) {
      if (/(\/|X)/.test(data.prevRoll))
        rollScore *= 2;
      if (/X/.test(data.prevRoll))
        rollScore += calcRoll(rolls[index+1], roll);
    } 
    data.total += rollScore;
    data.prevRoll = roll;
    return index === rolls.length - 1 ? data.total : data;
  }, {total: 0});
}

function calcRoll(roll, prevRoll) {
  return /[0-9]/.test(roll) ? parseInt(roll) :
    /\//.test(roll) ? 10 - prevRoll :
      /X/.test(roll) ? 10 : 0;
}


// assertions

console.log(calculateScore('12345123451234512345') === 60);
console.log(calculateScore('XXXXXXXXXXXX') === 300);
console.log(calculateScore('90909090909090909090') === 90);
console.log(calculateScore('5/5/5/5/5/5/5/5/5/5/5') === 150);
console.log(calculateScore('X9/X9/X9/X9/X9/X') === 200);