<canvas width="600" height="400"></canvas>
<script>
var tela = document.querySelector('canvas');
var pincel = tela.getContext('2d');
pincel.fillStyle = 'grey';
pincel.fillRect(0, 0, 600, 400);
function limparTela() {
pincel.fillStyle = 'grey';
pincel.fillRect(0, 0, 600, 400);
}
function exibeAlerta(mouse) {
// alert(mouse);
console.log(mouse)
pincel.fillStyle = 'darkblue';
pincel.beginPath();
pincel.arc(mouse.clientX, mouse.clientY, 20, 0, 10 * 3.14);
pincel.fill();
}
tela.onmousemove = exibeAlerta;
tela.onmouseout = limparTela;
pincel.fillRect(0, 0, 600, 400);
</script>
