Pen draw

<!DOCTYPE html>
<html>
<head>
	<title></title>
</head>
<body>
<canvas width="500" height="500" id="canvas" onmousemove="createLines(event);"></canvas>
<script type="text/javascript">
	var canvas = document.getElementById("canvas");
	var board = canvas.getContext("2d");
	var createLines = function (event) {
		board.clearRect(0,0,500,500);
		var thisevent = this.event;
		board.strokeStyle = "black";
		board.lineWidth = 1;
		board.beginPath();
		board.moveTo(thisevent.clientX,thisevent.clientX);
		board.lineTo(thisevent.clientX--, thisevent.clientY--);
		board.stroke();

	}


</script>
</body>
</html>