bandeiras.html

<canvas id="tela" width="1200" height="400"></canvas>

<script>

var tela = document.getElementById("tela");
var c = tela.getContext("2d");

c.fillStyle = "yellow";
c.fillRect(0,0,600,200);

c.fillStyle = "blue";
c.fillRect(0,200,600,100);

c.fillStyle = "red";
c.fillRect(0,300,600,100);

c.fillStyle = "red";
c.fillRect(800,0,400,200);

c.fillStyle = "green";
c.fillRect(800,200,400,200);

</script>