Jquery attr not working properly for Checkbox Required attribute

I try to toggle text box on checkbox's click event and it working fine. My Issue is that I also want to change checkbox's required attribute.

Here is my code which will remove required attribute but can not toggle it.

 $('#sender_name').change(function(event){

    if ($('#sender_name').attr('required', 'required'))
    {
        $('#sender_name').removeAttr('required', 'required');
    }
    else
    {
        $('#sender_name').attr('required', 'required');
    }

    $('.sender_name_text').toggle();
});

Using this code, checkbox's attribute will removed, but not appy again. check it in fiddle by inspect element.

Here Is Fiddle Link

-- Regards