var text = "";
var i = 0; // 초기식
while (i < 10) {
text += i + "<br>";
i++;
}
document.getElementById("demo").innerHTML = text;
<!DOCTYPE html>
<html lang="ko">
<head></head>
<body>
<h1>JavaScript while</h1>
<p id="demo"></p>
</body>
</html>