I have a canvas element defined statically in the html with a width and height. If I attempt to use JavaScript to resize it dynamically (setting a new width and height - eit
I just had the same problem as you, but found out about the toDataURL method, which proved useful.
The gist of it is to turn your current canvas into a dataURL, change your canvas size, and then draw what you had back into your canvas from the dataURL you saved.
So here's my code:
var oldCanvas = canvas.toDataURL("image/png");
var img = new Image();
img.src = oldCanvas;
img.onload = function (){
canvas.height += 100;
ctx.drawImage(img, 0, 0);
}