Filtered text field using javascript

<script type="text/javascript" language="javascript">

    function getkey(e) {

        if (window.event)

            return window.event.keyCode;

        else if (e)

            return e.which;

        else

            return null;

    }

    function goodchars(e, goods) {

        // alert(e.value);

        var key, keychar;

        key = getkey(e);

        if (key == null) return true;

        keychar = String.fromCharCode(key);

        if (goods.indexOf(keychar) != -1)

            return true;

        if (key == null || key == 0 || key == 8 || key == 9 || key == 13 || key == 27 || key == 40 || key == 41 || key == 32 || key == 45)

            return true;

        return false;

    }

</script>

<input name="textfield5" type="text" class="pTable" id="textPrimphone" runat="server" onkeypress="return goodchars(event,'1234567890')" />