Ejercicio bandera
<canvas width="600" height="400"></canvas>
<script>
    var pantalla = document.querySelector("canvas");
    var pincel = pantalla.getContext("2d");
    /*
    pincel.fillStyle = "lightgrey";//Propiedad
    pincel.fillRect(0,0,600,400);//funcion
    */
    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*3.14);
    pincel.fill();
</script>