限制文本框只能输入数字

HTML代码：

<input type="text" name="age" value="0" size="3" maxlength="3" onkeypress = "KeyPress(this);"/>

JS代码：

<script language = "javascript">
function KeyPress(objTR)
{
var txtval = objTR.value;
var key = event.keyCode;

if((key < 48 || key >57))
{
event.keyCode = 0;
}
}
</script>