Uncaught TypeError: Cannot read property 'getContext' of undefined
<p>I get this error "Uncaught TypeError: Cannot read property 'getContext' of undefined " while running script. It seems that variable "canvas" is undefined but I can't figure out why.</p>

<pre><code>var world = {
    canvas: document.getElementById("myCanvas"),
    context: this.canvas.getContext("2d"),
    centerX: this.canvas.width / 2,
    centerY: this.canvas.height / 2,
    drawShape: function (shape) {
        if (typeof shape.draw() === "function")
            shape.draw();
    }
};
</code></pre>