判斷input中輸入的是否是數字

<form action="<%=basepath%>/admin/t_hotel/checkLicence"
			enctype="multipart/form-data" method="post" "return checkNum();">
<input type="text" name="stbCount" required="required" id="stbMaxCount"/>
</form>

<script type="text/javascript">
	
		function checkNum() {
			var info="";
			var stbCount = document.getElementById("stbMaxCount").value;
			if (isNaN(stbCount)) {
				info+="終端最大數量請填寫數字！"+stbCount;
				modalDialogAlert(info);
				return false;
			} else {
				return true;
			}
		}
	</script>