function restrictByPattern(myfield, e, restrictionType) {
    if (!e) var e = window.event
    if (e.keyCode) code = e.keyCode;
    else if (e.which) code = e.which;
    var character = String.fromCharCode(code);
    // if they pressed esc... remove focus from field...
    if (code == 27) { this.blur(); return false; }
    // ignore if they are press other keys
    // strange because code: 39 is the down key AND ' key...
    // and DEL also equals .
    if (!e.ctrlKey && code != 9 && code != 8 && code != 36 && code != 37 && code != 38 && (code != 39 || (code == 39 && character == "'")) && code != 40) {
        if (character.match(restrictionType)) {
            return true;
        } else {
            return false;
        }
    }
}

function restrictByLength(field, length) {
    return (field.value.length <= length);
}

function restrictPhoneNumber(field, e) {
    var restriction = (field.value.length > 0) ? '[0-9]' : '[1-9]';
    return restrictByPattern(field, e, restriction);
}