Solution to eloquentjavascript exercise second 2nd edition (Chapter 7) eloquent javascript

eloquentjavascript_solutions_chapter_7.js

function Plant() {
    this.energy = 3 + Math.random() * 4;
}
Plant.prototype.act = function(context) {
    if (this.energy > 19) {
        var space = context.find(" ");
        if (space)
            return {type: "reproduce", direction: space};
    }
    if (this.energy < 20)
        return {type: "grow"};
};
function PlantEater() {
    this.energy = 20;
    this.direction = randomElement(Object.keys(directions));
    this.eatCounter = 1;
}
PlantEater.prototype.act = function(context) {
    var space = context.find(" ");
    if (this.energy > 40 && space)
        return {type: "reproduce", direction: space};
    var plant = context.findAll("*");
    if (plant.length > 1) {
        if (this.eatCounter >= 0) {
            this.eatCounter = 0;
            return {type: "eat", direction: randomElement(plant)};
        } else {
            this.eatCounter++;
        }
    }
    if (space) {
        var spaces = context.findAll(" ");
        if (spaces.indexOf(this.direction) == -1) {
            this.direction = space;
        }
        return {type: "move", direction: this.direction};
    } else {
        this.direction = "s";
    }
};
function Tiger() {
    this.energy = 40 + Math.random() * 10;
    this.direction = randomElement(Object.keys(directions));
}
Tiger.prototype.act = function (context) {
    var space = context.find(" ");
    var critter = context.find("O");
    if (critter) {
        return {type: "eat", direction: critter};
    }
    if (this.energy > 50 && space) {
        return {type: "reproduce", direction: space};
    }
    if (space) {
        var spaces = context.findAll(" ");
        if (spaces.indexOf(this.direction) == -1) {
            this.direction = space;
        }
        return {type: "move", direction: this.direction};
    } else {
        this.direction = "s";
    }
}

var legend = {
    "#": Wall,
    "@": Tiger,
    "O": PlantEater,
    "*": Plant};

var valley = new LifelikeWorld(
       [
           "####################################################",
           "#                 ####         ****              ###",
           "#   *  @  ##                 ########       OO    ##",
           "#   *    ##        O O                 ****       *#",
           "#       ##*                        ##########     *#",
           "#      ##***  *         ****                     **#",
           "#* **  #  *  ***  @   #########                  **#",
           "#* **  #      *               #   *              **#",
           "#     ##              #   O   #  ***@         ######",
           "#*            @       #       #   *        O  #    #",
           "#*                    #  ######                 ** #",
           "###          ****          ***                  ** #",
           "#       O                        @         O       #",
           "#   *     ##  ##  ##  ##               ###      *  #",
           "#   **         #   @          *       #####  O     #",
           "##  **  O   O  #  #    ***  ***        ###      ** #",
           "###               #   *****                    ****#",
           "####################################################"],
    legend
);
console.log(valley.toString());
for (var i = 0; i < 1000; i++) {
    valley.turn();
    console.log(valley.toString());
}