<canvas width="600" heigth="400"> </canvas>
<script>
var pantalla = document.querySelector("canvas");
var pincel = pantalla.getContext("2d");
pincel.fillStyle = "yellow"
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();
pincel.fillStyle = "purple";
pincel.beginPath();
pincel.arc(300,200,50,0,2*3.14);
pincel.fill();
</script>
