[jQuery] how disable text box based on "select" setting

[stvwlf]

Hi

I am new to jQuery - appreciate some help.

I found some code that hides a textbox when a dropdown is set to a
specific value.  That works fine.

        $(document).ready(function(){
                if($('select[name=costType] :selected').val() == 'fr'){
                        $('input[name=costValue]').disabled();
                }
        });

What I would like to do is not hide the textbox but disable it.  I
would also like text box's contents cleared when it is being
disabled.  If the user goes back and selects a different value in the
dropdown, the textbox to be enabled, with no value in it.

The dropdown name is costType and it has 3 possible values.  Only one
of them is to trigger disabling the text box.

Thank you for your help
Steve