<meta charset="UTF-8">
<script>
function pulaLinha() {
document.write("<br><br>");
}
function mostra(frase) {
document.write(frase);
pulaLinha();
}
var n = 20;
while(n <= 20 && n >= 0) {
mostra(n);
n = n - 1;
}
mostra("FIM");
</script>