<canvas width="600" height="400">
</canvas>
<script>
var pantalla = document.querySelector("canvas");
var pincel = pantalla.getContext("2d");
pincel.fillStyle = "lightgrey";
pincel.fillRect(0, 0, 600, 400);
pincel.fillStyle = "green";
pincel.fillRect(0, 0, 200, 400);
pincel.fillStyle = "red";
pincel.fillRect(400, 0, 200, 400);
pincel.fillStyle = "yellow";
pincel.beginPath();
pincel.moveTo(300, 200);
pincel.lineTo(200, 400);
pincel.lineTo(400, 400);
pincel.fill();
pincel.fillStyle = "blue";
pincel.beginPath();
pincel.arc(300, 200, 50, 0, 2*Math.PI);
pincel.fill();
</script>
