function getKeyCode(e) {
    if (window.event)
        return window.event.keyCode;
    else if (e)
        return e.which;
    else
        return null;
}

function validateKey(e) {
    var key = getKeyCode(e);

    if (key == null) return true;

    // Digits
    // Comment / remove this "if" statement if you don't want to allow digits
    if (key >= 48 && key <= 57) {
        return true;
    }

    // Letters
    // Comment / remove this "if" statement if you don't want to allow letters
    //    if ((key >= 65 && key <= 90) || (key >= 97 && key <= 122)) {
    //        return true;
    //    }


    if (key == null || key == 0 || key == 8 || key == 9 || key == 13 || key == 27) {
        return true;
    }

    return false;
}