.gitignore

/node_modules

gol.js

Array.prototype.hasCell = function(cell) {
    if (arguments.length == 2) cell = new Cell(arguments[0], arguments[1]);
    return this.filter(function(c) {
        return c.x == cell.x && c.y == cell.y;
    }).length > 0;
};

function World(cells) {
    this.cells = cells || [];
}

World.prototype.advanceStep = function() {
    var candidates = this.computeCandidates(),
        newState = [];

    candidates.forEach(function(cell) {
        var neighbours = this.findNeighbours(cell);
        if (neighbours.length == 2 && this.cells.hasCell(cell) || neighbours.length == 3)
            newState.push(cell);
    }, this);

    this.cells = newState;
};

World.prototype.computeCandidates = function() {
    var candidates = [];
    this.cells.forEach(function(cell) {
        for (var t = 0; t < 9; t++) {
            var x = (t % 3) - 1, y = Math.floor(t / 3) - 1,
                c = new Cell(cell.x + x, cell.y + y);
            if (!candidates.hasCell(c))
                candidates.push(c);
        }    
    }, this);
    return candidates;
};

World.prototype.findNeighbours = function(reference) {
    var neighbours = [];
    for (var y = reference.y - 1; y <= reference.y + 1; y++)
        for (var x = reference.x - 1; x <= reference.x + 1; x++) {
            if (x == reference.x && y == reference.y) continue;
            var c = new Cell(x, y);
            if (this.cells.hasCell(c)) neighbours.push(c);
        }
    return neighbours;
};

World.prototype.render = function() {
    var bounds = this.getBoundingBox(),
        screen = '';
    for (var y = bounds.top; y <= bounds.bottom; y++) {
        for (var x = bounds.left; x <= bounds.right; x++) {
            screen += (this.cells.hasCell(x, y)) ? 'X' : ' ';
        }
        screen += '\n';
    }
    console.log(screen);
};

World.prototype.getBoundingBox = function() {
    var bounds = {
        left   : Infinity,
        top    : Infinity,
        right  : -Infinity,
        bottom : -Infinity
    };
    this.cells.reduce(function(u, v) {
        u.left   = Math.min(u.left, v.x);
        u.top    = Math.min(u.top, v.y);
        u.right  = Math.max(u.right, v.x);
        u.bottom = Math.max(u.bottom, v.y);
        return u;
    }, bounds);
    return bounds;
};

World.parse = function(source) {
    var cells = [];
    source.split('\n').forEach(function(line, y) {
        for (var x = 0; x < line.length; x++) {
            if (line[x] != ' ') cells.push(new Cell(x, y));
        }
    }, this);
    return new World(cells);
};

function Cell(x, y) {
    this.x = x;
    this.y = y;
}

module.exports = {
    World : World,
    Cell  : Cell
};

main.js

var fs = require('fs');
var gol   = require('./gol'),
    World = gol.World,
    Cell  = gol.Cell;


var w = World.parse(fs.readFileSync('pattern.txt', 'utf8'));

while(true) {
    w.render();
    w.advanceStep();
}

pattern.txt

xxxxxxxx xxxxx   xxx      xxxxxxx xxxxx

test.js

require('chai').should();
var gol   = require('./gol'),
    World = gol.World,
    Cell  = gol.Cell;


describe('known patterns', function() {

    describe('square', function() {

        it('should be static', function() {
            var w = new World([
                new Cell(0,0),
                new Cell(1,0),
                new Cell(0,1),
                new Cell(1,1)
            ]);

            w.advanceStep();
            w.cells.length.should.equal(4);
            w.cells.hasCell(0,0).should.be.true;
            w.cells.hasCell(1,0).should.be.true;
            w.cells.hasCell(0,1).should.be.true;
            w.cells.hasCell(1,1).should.be.true;
        });

        it('should have alternating lines', function() {
            var w = new World([
                new Cell(1, 0),
                new Cell(1, 1),
                new Cell(1, 2)
            ]);

            w.advanceStep();
            w.cells.length.should.equal(3);
            w.cells.hasCell(0,1).should.be.true;
            w.cells.hasCell(1,1).should.be.true;
            w.cells.hasCell(2,1).should.be.true;

            w.advanceStep();
            w.cells.length.should.equal(3);
            w.cells.hasCell(1,0).should.be.true;
            w.cells.hasCell(1,1).should.be.true;
            w.cells.hasCell(1,2).should.be.true;
        });

        it('should return a valid bounding box', function() {
            var w = new World([
                new Cell(0,0),
                new Cell(3,4)
            ]);

            var box = w.getBoundingBox();
            box.left.should.equal(0);
            box.top.should.equal(0);
            box.right.should.equal(3);
            box.bottom.should.equal(4); 
        });

        

    });

});