Bowling Game Kata

Uncle Bob's classic implemented in JavaScript

Scoring bowling

The game consists of 10 frames as shown above. In each frame the player has two opportunities to knock down 10 pins. The score for the frame is the total number of pins knocked down, plus bonuses for strikes and spares.

A spare is when the player knocks down all 10 pins in two tries. The bonus for that frame is the number of pins knocked down by the next roll. So in frame 3 above, the score is 10 (the total number knocked down) plus a bonus of 5 (the number of pins knocked down on the next roll.)

A strike is when the player knocks down all 10 pins on his first try. The bonus for that frame is the value of the next two balls rolled.

In the tenth frame a player who rolls a spare or strike is allowed to roll the extra balls to complete the frame. However no more than three balls can be rolled in tenth frame.

The requirements

• Write class "BowlingGame" that has two methods
  • roll(pins)
    • called each time the player rolls a ball. The argument is the number of pins knocked down.
  • score()
    • called only after the very end of the game. Returns total score of the game.

Quick design session

One game
A game has 10 frames
A frame has one or two rolls
The tenth frame has two or three rolls. It's different from all the other frames
The score function must iterate through all the frames, and calculate all their scores
The score for a spare or a strike depends on the frames successor

Begin

• Create directory bowling-game
• Create bowlingGame.js
• Create bowlingGame-tests.js

// bowlingGame-tests.js
describe("BowlingGame", function() {
	
});

Install and configure karma test-runner

npm install -g karma
npm install -g karma-mocha
npm install -g karma-chai
karma init

	Testing framework: mocha
	Require.js: no
	Capture browser: PhantomJS
	Source and test files: *.js
	Excluded:
	Run tests on change: yes

Open the created configuration file and change frameworks: ['mocha'], to frameworks: ['mocha', 'chai'],.
Kick-start the test runner typing karma start and hitting ENTER

The first test

describe("BowlingGame", function() {
	it("handle gutter game", function() {
		var game = new BowlingGame();
		for (var i = 0; i < 20; i++) {
			game.roll(0);
		}
		expect(game.score()).to.equal(0);
	});
});

The second test

describe("BowlingGame", function() {
	var game;

	beforeEach(function(){
		game = new BowlingGame();
	});

	function rollMany (n, pins) {
		for (var i = 0; i < n; i++) {
			game.roll(pins)
		}
	}

	it("handle gutter game", function() {
		rollMany(20, 0);
		expect(game.score()).to.equal(0);
	});

	it("should handle all ones", function() {
		rollMany(20, 1);
		expect(game.score()).to.equal(20);
	});
});

The third test

describe("BowlingGame", function() {
	var game;

	beforeEach(function(){
		game = new BowlingGame();
	});

	function rollMany (n, pins) {
		for (var i = 0; i < n; i++) {
			game.roll(pins)
		}
	}

	function rollSpare() {
		game.roll(5);
		game.roll(5);
	}

	it("handle gutter game", function() {
		rollMany(20, 0);
		expect(game.score()).to.equal(0);
	});

	it("should handle all ones", function() {
		rollMany(20, 1);
		expect(game.score()).to.equal(20);
	});

	it("should handle one spare", function() {
		rollSpare();
		game.roll(3);
		rollMany(17, 0);
		expect(game.score()).to.equal(16);
	});
});

The fourth test

describe("BowlingGame", function() {
	var game;

	beforeEach(function(){
		game = new BowlingGame();
	});

	function rollMany (n, pins) {
		for (var i = 0; i < n; i++) {
			game.roll(pins)
		}
	}

	function rollSpare() {
		game.roll(5);
		game.roll(5);
	}

	function rollStrike() {
		game.roll(10);
	}

	it("should handle gutter game", function() {
		rollMany(20, 0);
		expect(game.score()).to.equal(0);
	});

	it("should handle all ones", function() {
		rollMany(20, 1);
		expect(game.score()).to.equal(20);
	});

	it("should handle one spare", function() {
		rollSpare();
		game.roll(3);
		rollMany(17, 0);
		expect(game.score()).to.equal(16);
	});

	it("should handle one strike", function() {
		rollStrike();
		game.roll(3);
		game.roll(4);
		rollMany(16, 0);
		expect(game.score()).to.equal(24);
	});
});

The fifth test

describe("BowlingGame", function() {
	var game;

	beforeEach(function(){
		game = new BowlingGame();
	});

	function rollMany (n, pins) {
		for (var i = 0; i < n; i++) {
			game.roll(pins)
		}
	}

	function rollSpare() {
		game.roll(5);
		game.roll(5);
	}

	function rollStrike() {
		game.roll(10);
	}

	it("should handle gutter game", function() {
		rollMany(20, 0);
		expect(game.score()).to.equal(0);
	});

	it("should handle all ones", function() {
		rollMany(20, 1);
		expect(game.score()).to.equal(20);
	});

	it("should handle one spare", function() {
		rollSpare();
		game.roll(3);
		rollMany(17, 0);
		expect(game.score()).to.equal(16);
	});

	it("should handle one strike", function() {
		rollStrike();
		game.roll(3);
		game.roll(4);
		rollMany(16, 0);
		expect(game.score()).to.equal(24);
	});

	it("should handle a perfect game", function() {
		rollMany(12, 10);
		expect(game.score()).to.equal(300);
	});
});

Final code

var BowlingGame = function() {
	this.rolls = [];
	this.currentRoll = 0;
};

BowlingGame.prototype.roll = function(pins) {
	this.rolls[this.currentRoll++] = pins;
};

BowlingGame.prototype.score = function() {
	var score = 0;
	var frameIndex = 0;
	var self = this;

	function sumOfBallsInFrame() {
		return self.rolls[frameIndex] + self.rolls[frameIndex + 1];
	}

	function spareBonus() {
		return self.rolls[frameIndex + 2];
	}

	function strikeBonus() {
		return self.rolls[frameIndex + 1] + self.rolls[frameIndex + 2];
	}

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

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

	for (var frame = 0; frame < 10; frame++) {
		if (isStrike()) {
			score += 10 + strikeBonus();
			frameIndex++;
		} else if (isSpare()) {
			score += 10 + spareBonus();
			frameIndex += 2;
		} else {
			score += sumOfBallsInFrame();
			frameIndex += 2;
		}
	}
	return score;
};