<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 = 'blue';
pincel.beginPath();
pincel.moveTo(300,200);
pincel.lineto(200,400);
pincel.lineto(400,400);
pincel.fill();
</script>
