JS 遍历头字母添加滚动条

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
function f() {
var divs = document.getElementsByTagName("div");
for(var i = 0; i < divs.length; i++) {
var id = divs[i].id;
if (typeof(id) != "undefined") {
if (id.charAt(0) == "H")
divs[i].style.overflowX = "scroll";
else if (id.charAt(0) == "V")
divs[i].style.overflowY = "scroll";
else if (id.charAt(0) == "X")
divs[i].style.display = "none";
}
}
}
</script>
</head>
<body>
<div id="Horizontal" style="width:100px; height: 100px;">1</div>
<div id="Vertical1" style="width:100px; height: 100px">2</div>
<div id="Vertical2" style="width:100px; height: 100px">3</div>
<div id="Xhide" style="width:100px; height: 100px">4</div>
<input type="button" value="click" onclick="f()">
</body>
</html>