写法一:
<script type="text/javascript">
function checknum(){
var obj = document.getElementById("num");
var reg = new RegExp("^[0-9]*$");
if(!reg.test(obj.value)) alert("请输入数字!");
}
</script>
写法二:
<script type="text/javascript">
function checknum(){
var obj = document.getElementById("num");
if(!/^[0-9]*$/.test(obj.value)) alert("请输入数字!");
}
</script>