If this renders correctly you should see one big friendly green square.
<canvas id="canvas" width="200" height="200" ></canvas>
<canvas id="canvas2" width="200" height="200" style="display:none" ></canvas>
<script>
var canvas = document.getElementById("canvas");
var canvas2 = document.getElementById("canvas2");
var context = canvas.getContext("2d");
var context2 = canvas2.getContext("2d");
context2.fillStyle = 'red';
context2.fillRect(0,0,200,200);
context2.fillStyle = 'green';
context2.fillRect(50,50,100,100);
context.drawImage(canvas2, 50, 50, 100, 100, 0, 0, 200, 200);
</script>