The application runs faster after the prototype property of the GameObject is defined. As a direct result, every instance of GameObject references the methods within GameObject.prototype, taking them as their own methods.

// define the GameObject constructor function
var GameObject = function(width, height) {
    this.x = Math.floor((Math.random() * myCanvasWidth) + 1);
    this.y = Math.floor((Math.random() * myCanvasHeight) + 1);
    this.width = width;
    this.height = height;
    return this;
};

// (re)define the GameObject prototype object
GameObject.prototype = {
    x: 0,
    y: 0,
    width: 5,
    width: 5,
    draw: function() {
        myCanvasContext.fillRect(this.x, this.y, this.width, this.height);
    }
};

We can then instantiate the GameObject 100 times.

var x = 100,
arrayOfGameObjects = [];

do {
    arrayOfGameObjects.push(new GameObject(10, 10));
} while(x--);

When we call the draw method, it will reference the exact same function.

var GameLoop = function() {
    for(gameObject in arrayOfGameObjects) {
        gameObject.draw();
    }
};