startGame.js

function startGame() {

    myGamePiece = new Circle(300, 240,20,"blue");
    myObstacle  = new  Circle(rand(), 0, 20, "red");

    myGameArea.start();
}
var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.context = this.canvas.getContext("2d");
        this.canvas.width = 600;
        this.canvas.height = 270;
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.interval = setInterval(updateGameArea, 30);
        window.addEventListener('keydown', function (e) {
            myGameArea.keys = (myGameArea.keys || []);
            myGameArea.keys[e.keyCode] = true;
        })
        window.addEventListener('keyup', function (e) {
            myGameArea.keys[e.keyCode] = false;
        })
    },
    clear : function() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    }
}