A CodePen by pawelmhm.

index.html

  <canvas id="canvas" width="600" height="600"></canvas>

script.js

function Cell(x, y, size) {
    this.x = x;
    this.y = y;
    this.size = 10;
    this.neighbors = [];
}
Cell.prototype = {
    constructor: Cell,
    sayName: function () {
        return [this.x, this.y];
    },
    getX: function () {
        return this.x;
    },
    getY: function () {
        return this.y;
    },
};

function Empty(x, y) {
    Cell.call(this, x, y);
    this.state = 0;
    this.colour = '#000';
}
Empty.prototype = new Cell();

function Tree(x, y) {
    Cell.call(this, x, y);
    this.state = 1;
    this.colour = '#00CC33';
}
Tree.prototype = new Cell();

function BurningTree(x, y) {
    Cell.call(this, x, y);
    this.state = 2;
    this.colour = '#FF0000';
}
BurningTree.prototype = new Cell();

function Forest(sizeX, sizeY, canvas, probOfFire, probOfGrowth) {
    this.sizeX = sizeX;
    this.sizeY = sizeY;
    this.cells = [];
    this.canvas = canvas;
    this.cx = canvas.getContext('2d');
    this.probOfFire = probOfFire;
    this.probOfGrowth = probOfGrowth;
}
Forest.prototype = {
    constructor: Forest,
    addCell: function (newCell) {
        this.cells.push(newCell);
        this.drawCell(newCell);
    },
    removeCell: function (cell) {
        var cut = this.cells.indexOf(cell);
        this.cells.splice(cut, 1);
    },
    growTree: function (emptyCell) {
        var diceNature = Math.random();
        if (diceNature < this.probOfGrowth) {
            var x = emptyCell.getX();
            var y = emptyCell.getY();
            this.removeCell(emptyCell);
            var newTree = new Tree(x, y);
            this.addCell(newTree);
        }
    },
    burnTree: function (tree) {
        var dice = Math.random();
        /* var neighbors = this.getNeighbors(tree);
        for (i = 0; i < neighbors.length; i++) {
            if (neighbors[i] instanceof BurningTree) {
                var neighborBurning = true;
                break;
            }
        } */
        if ((dice < this.probOfFire)) {
            var x = tree.x;
            var y = tree.y;
            this.removeCell(tree);
            var newBurningTree = new BurningTree(x, y);
            this.addCell(newBurningTree);
        }
    },
    endBurning: function (burningTree) {
        var x = burningTree.x;
        var y = burningTree.y;
        this.removeCell(burningTree);
        var newEmpty = new Empty(x, y);
        this.addCell(newEmpty);
    },
    getAllCells: function () {
        return this.cells;
    },
    updateForest: function () {
        for (i = 0; i < this.cells.length; i++) {
            if (this.cells[i] instanceof Tree) {
                var tree = this.cells[i];
                this.burnTree(tree);
            } else if (this.cells[i] instanceof BurningTree) {
                var burningTree = this.cells[i];
                this.endBurning(burningTree);
            } else if (this.cells[i] instanceof Empty) {
                var empty = this.cells[i];
                this.growTree(empty);
            }
        }
    },
    drawSquare: function (cx, posX, posY, size, color) {
        cx.fillStyle = color;
        cx.fillRect(posX, posY, size, size);
    },
    drawCircle: function (cx, posX, posY, size, color) {
        var centerX = posX;
        var centerY = posY;
        var radius = size / 2;

        cx.beginPath();
        cx.arc(centerX, centerY, radius, 0, 2 * Math.PI, false);
        cx.fillStyle = color;
        cx.fill();
        cx.lineWidth = 2;
        cx.strokeStyle = '#000';
        cx.stroke();
    },
    drawCell: function (cell) {
        var posX = cell.x;
        var posY = cell.y;
        var colour = cell.colour;
        var size = cell.size;

        this.drawSquare(this.cx, posX, posY, size, colour);

        /* this.drawCircle(this.cx, posX, posY, size, colour);*/

    },
    populate: function (cell) {
        var width = this.canvas.width;
        var height = this.canvas.height;
        var numOfSquares = (width * height) / (cell.size * cell.size);
        var i = 0;
        var posX = 0;
        var posY = 0;
        while (i < numOfSquares) {
            if (posX >= width - cell.size) {
                posY += cell.size + 2;
                posX = 0;
            }
            var e = new Tree(posX, posY);
            this.addCell(e);
            posX += cell.size + 1;
            i += 1;
        }
    },
    getNeighbors: function (cell) {
        var width = this.sizeX;
        var height = this.sizeY;
        var neighbors = [];
        var position = this.cells.indexOf(cell);
        neighbors.push(this.cells[position - 1]);
        neighbors.push(this.cells[position + 1]);
        neighbors.push(this.cells[position + (width / cell.size)]);
        neighbors.push(this.cells[position - (width / cell.size)]);
        neighbors.push(this.cells[position + (width / cell.size + cell.size)]);
        neighbors.push(this.cells[position + (width / cell.size - cell.size)]);
        console.log(neighbors);
        return neighbors;
    }
};
cx = document.getElementById('canvas');

function deadForest() {
    las = new Forest(cx.width, cx.height, cx, 0.1, 0.0);
    cell = new Cell(0, 0);
    las.populate(cell);
    window.setInterval(refresh, 520);

    function refresh() {
        las.updateForest();
    }
}

function forestWithNoFire() {
    las = new Forest(cx.width, cx.height, cx, 0.03, 1);
    cell = new Cell(0, 0);
    las.populate(cell);
    window.setInterval(refresh, 520);

    function refresh() {
        las.updateForest();
    }
}

function forestWithFires() {
    las = new Forest(cx.width, cx.height, cx, 0.2, 1);
    cell = new Cell(0, 0, 20);
    las.populate(cell);
    window.setInterval(refresh, 520);

    function refresh() {
        las.updateForest();
    }
}

deadForest();
//forestWithNoFire();
//forestWithFires();

style.css

/* 

Forest Fire --> 2d cellular automaton 
A small exercise in dealing with JS objects.

Green square = tree;
red = burning tree;
black = empty space;

More on this particular programming challenge:

http://rosettacode.org/wiki/Forest_fire

More on cellular automata:

http://en.wikipedia.org/wiki/Cellular_automaton

*/