숫자인지 확인하는 jquery 메소드

<script language="javascript">
var t=$("#id").val();//这个就是我们要判断的值了
if(!isNaN(t)){
  alert("是数字");
}else{
  alert("不全是数字");
}
</script>

<script type="text/javascript">
var test1= new Boolean(true);
var test2= new Boolean(false);
var test3= new Date();
var test4= new String("999");
var test5= new String("999 888");
document.write(Number(test1)+ "<br />");
document.write(Number(test2)+ "<br />");
document.write(Number(test3)+ "<br />");
document.write(Number(test4)+ "<br />");
document.write(Number(test5)+ "<br />");
</script>

1
0
1256657776588
999
NaN