สามารถใช้ formatnumber ร่วมกับ getelement ได้หรือเปล่าครับ

<script type="text/javascript">
//<![CDATA[
    function KeyPress(e) {
        var keynum;
        var keychar;
        var numcheck;

        if (window.event) // IE
        {
            keynum = e.keyCode;
        }
        else if (e.which) // Netscape/Firefox/Opera
        {
            keynum = e.which;
        }

        keychar = String.fromCharCode(keynum);
        numcheck = /\d|[\b]|[\.]/;

        return numcheck.test(keychar);
    }

    function KeyUp(txtBox) {
        var source = txtBox.value.replace(/,/gi, '').split('.', 2);
        var output = '';
        var decimal = '';
        var count = 0;

        if (source[0].length > 3) {
            while (source[0].length > 1 && source[0].substring(0, 1) == '0') source[0] = source[0].substring(1);
            count = (source[0].length % 3 == 0) ? 3 : source[0].length % 3;
            output = source[0].substring(0, count);
            for (var i = 0; i < (source[0].length / 3) - 1; i++) output += ',' + source[0].substring((i * 3) + count, (i * 3) + 3 + count);
            if (source[1] != null) decimal = '.' + source[1];

        }
        else {
            source[0] = (source[0] == '' && txtBox.value.substring(0, 1) == '.') ? '0' : source[0];
            output = (source[0].length > 1 && source[0].substring(0, 1) == '0') ? source[0].replace(/0/i, '') : source[0];
            decimal = (source[1] != null) ? '.' + source[1] : '';

        }

        txtBox.value = output + decimal;
    }

//]]>
</script>

<input name="TextBox1" type="text" id="TextBox1" onkeypress="javascript:return KeyPress(event);" onkeyup="javascript:KeyUp(this);" />