怎样在文本框中只输入数字和小数点，连汉字都不让输入

具体代码如下:(这个是验证只能输入数字,不能输入其它字符的)
function CalcKeyCode(aChar)
{
var character=aChar.substring(0,1);
var code=aChar.charCodeAt(0);
return code;
}

function checkNumber(val)
{
var strPass=val.value;
var strLength=strPass.length;
var lchar=val.value.charAt((strLength)-1);
var cCode=CalcKeyCode(lchar);

if(cCode<48 || cCode>57)
{
var myNumber=val.value.substring(0,(strLength)-1);
val.value=myNumber;
}
return false;
}

<script type="text/javascript" src="validNum.js"></script>
<form name="myForm" method="post" action="#">
Enter an integer here:<input name="txtNumber" type="text" id="txtNumber" onKeyUp="javascript:checkNumber(myForm.txtNumber);">
</form>