fluent-bowling-spec.coffee

describe "Bowling Scorer", ->
  describe "gutter game", ->
    Then -> expect(game.roll(0, 20).score()).toBe(0)

  describe "all 1's", ->
    Then -> expect(game.roll(1, 20).score()).toBe(20)

  describe "spare", ->
    Then -> expect(game.roll(5, 2).roll(3).roll(0, 17).score()).toBe(16)

  describe "strike", ->
    Then -> expect(game.roll(10).roll(3).roll(4).roll(0, 16).score()).toBe(24)

  describe "perfect game", ->
    Then -> expect(game.roll(10, 22).score()).toBe(300)

fluent-bowling.js

(function () {
  function game(initialRolls, currentFrame) {
    return {
      roll: game.roll,
      score: game.score,
      _rolls: initialRolls || initializeRolls(),
      _currentFrame: currentFrame || 0
    };
  }

  game.roll = function (pins, numberOfRolls) {
    var i,
    rolls = _.clone(this._rolls);
    currentFrame = this._currentFrame;

    if (numberOfRolls === undefined) { numberOfRolls = 1; }

    for (i = 0; i < numberOfRolls; i += 1) {
      rolls[currentFrame] = pins;
      currentFrame += 1;
    }
    return game(rolls, currentFrame);
  };

  game.score = function () {
    var i,
    frameIndex = 0,
    result = 0,
    rolls = this._rolls;

    for (i = 0; i < 10; i += 1) {
      if(isStrike(frameIndex, rolls)) {
        result += scoreStrikeFrame(frameIndex, rolls);
        frameIndex += 1;
      } else if(isSpare(frameIndex, rolls)) {
        result += scoreSpareFrame(frameIndex, rolls);
        frameIndex += 2;
      } else {
        result += scoreOpenFrame(frameIndex, rolls);
        frameIndex += 2;
      }
    }
    return result;
  };

  function isStrike(frameIndex, rolls) {
    return rolls[frameIndex] === 10;
  }

  function scoreStrikeFrame(frameIndex, rolls) {
    return 10 + rolls[frameIndex + 1] + rolls[frameIndex + 2];
  }

  function isSpare(frameIndex, rolls) {
    return rolls[frameIndex] + rolls[frameIndex + 1] === 10;
  }

  function scoreSpareFrame(frameIndex, rolls) {
    return 10 + rolls[frameIndex + 2];
  }

  function scoreOpenFrame(frameIndex, rolls) {
    return rolls[frameIndex] + rolls[frameIndex + 1];
  }

  function initializeRolls() {
    var i, rolls = [];
    for (i = 0; i < 22; i += 1) {
      rolls[i] = 0;
    }
    return rolls;
  }

  window.game = game();
})();

Oops. Just noticed that I forgot the "use strict"; at the top of the containing function in fluent-bowling.js