[Sweet]

Может потому, что:

<canvas id='mc' onclick='mcp(this)' width='0' height='0'></canvas>
	<br/>
	<script>
	  var canvasContext = document.getElementById("mc").getContext("2d");
		for(var prop in canvasContext) {
			document.body.innerHTML += 'document.getElementById("mc").getContext("2d").' + prop + ' = ' + canvasContext[prop] + '<br/>\n';
		}
	</script>