I am creating canvas dynamically and drawing image on the same, so how to do it?

window.onload = function ()
{
        var img = new Image();
        img.src = "images/rope.png";
        canvas = document.createElement("canvas");
        canvas.id = "canvasTest";
        canvas.width = window.innerWidth;
        canvas.height = window.innerHeight;
        canvas.style.position = "absolute";
        canvas.style.border = "1px solid";
        context = canvas.getContext("2d");
        context.drawImage(img, 0, 0);
        document.body.appendChild(canvas);
    }