1检查是否是数字

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<script type="text/javascript">
function checkInput(){

            var no = document.getElementById('no').value;
   alert(no);
  var re=/^[-+]?d+(.d+)?$/;
  if (no.match(re) == null){
    alert("不是数字");
   return false;}
  else{
      alert("就是数字");
   return true;
  }
}
</script>
</HEAD>

<BODY>
    输入验证: <input type="text" id="no" />
<input type="submit" onclick="checkInput()" />

</BODY>
</HTML>