Bandeira do Brasil

<canvas width="600" height="400"></canvas>

<script>

    var tela = document.querySelector('canvas');
    var pincel = tela.getContext ('2d');

//retângulo verde

    pincel.fillStyle = 'green'
    pincel.fillRect (0,0, 600, 400);

//triangulo amarelo inferior
    pincel.fillStyle = 'yellow';
    pincel.beginPath();
    pincel.moveTo(500, 200);
    pincel.lineTo(50, 200);
    pincel.lineTo(275, 350);
    pincel.fill();

//triangulo amarelo superior
    pincel.fillStyle = 'yellow';
    pincel.beginPath();
    pincel.moveTo(500, 200);
    pincel.lineTo(50, 200);
    pincel.lineTo(275, 50);
    pincel.fill();

//Circulo azul
pincel.fillStyle = 'blue'
pincel.beginPath();
pincel.arc(275, 200, 100, 0, 2*3.14);
pincel.fill();

</script>