Paper Scissors Rock

A silly childs game can pose an interesting challenge for software development. Programming the game rules can be approached in many different ways, obviously you could hard code a bunch of “if statements” however this would be very messy and unsustainable if you needed to add complexity to the game later on, (such as adding new rules)

if (player1 == 'paper' && player2 == 'rock') {
	return 'player1 wins';
}

Don’t do this ^

The better way to solve this would be to implement a data structure built around the game rules.

Javascript — Data structure approach

var gamerules = {
	scissors: { label: 'scissors' },
	paper: { label: 'paper' },
	rock: { label: 'rock' }
};
gamerules.scissors.beats = gamerules.paper;
gamerules.paper.beats = gamerules.rock;
gamerules.rock.beats = gamerules.scissors;

function play(player1, player2) {
	console.log(`playing ${player1.label} vs ${player2.label}`);
	if (player1.beats === player2) {
		console.log('player 1 wins ');
	} else if (player2.beats === player1) {
		console.log('player 2 wins');
	} else {
		console.log('draw');
	}
}

The In the first section we define a ‘Gamerules’ data structure. This allows us to easily define the rules of the game by setting the ‘beats’ property on each option

gamerules.scissors.beats = gamerules.paper;
gamerules.paper.beats = gamerules.rock;
gamerules.rock.beats = gamerules.scissors;

In the second half we create a “Play” function which will evaluate player1 and player2 to determine which choice wins.

function play(player1, player2) {
	console.log(`playing ${player1.label} vs ${player2.label}`);
	if (player1.beats === player2) {
		console.log('player 1 wins ');
	} else if (player2.beats === player1) {
		console.log('player 2 wins');
	} else {
		console.log('draw');
	}
}

See below for an example of how to “Play” the game using this function

console.log('starting game');
var scissors = gamerules.scissors;
var paper = gamerules.paper;
var rock = gamerules.rock;

play(scissors, scissors);
play(scissors, paper);
play(scissors, rock);

play(paper, scissors);
play(paper, paper);
play(paper, rock);

play(rock, scissors);
play(rock, paper);
play(rock, rock);

var gamerules = {
	scissors: { label: 'scissors' },
	paper: { label: 'paper' },
	rock: { label: 'rock' }
};
gamerules.scissors.beats = gamerules.paper;
gamerules.paper.beats = gamerules.rock;
gamerules.rock.beats = gamerules.scissors;

function play(player1, player2) {
	console.log(`playing ${player1.label} vs ${player2.label}`);
	if (player1.beats === player2) {
		console.log('player 1 wins ');
	} else if (player2.beats === player1) {
		console.log('player 2 wins');
	} else {
		console.log('draw');
	}
}

console.log('starting game');
var scissors = gamerules.scissors;
var paper = gamerules.paper;
var rock = gamerules.rock;

play(scissors, scissors);
play(scissors, paper);
play(scissors, rock);

play(paper, scissors);
play(paper, paper);
play(paper, rock);

play(rock, scissors);
play(rock, paper);
play(rock, rock);