<meta charset="utf-8">
<canvas width="600" height="400"></canvas>
<script>
var tela = document.querySelector("canvas");
var pincel = tela.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 = 'white';
pincel.beginPath();
pincel.moveTo(300, 200);
pincel.lineTo(200, 400);
pincel.lineTo(400, 400);
pincel.fill();
</script>
