Jquery Disable Button if Textarea is empty

HTML

<input type="text" name="textField" />

<button class="add_field_button" " >Click for more variations:</button>

JavaScript

/* Jquery Disable Button if Textarea is empty */

$(document).ready(function () {
    $('.add_field_button').attr('disabled', false);
    $('input[type="text"],textarea').on('keyup', function () {
        var textarea_value = $("#texta").val();
        var text_value = $('input[name="textField"]').val();
        if (text_value != '') {
            $('input[type="submit"]').attr('disabled', false);
        } else {
            $('input[type="submit"]').attr('disabled', true);
        }
    });
});