Send html array as post variable using Request.JSON

Programmer Question

I have an html:

First name: 

Last name: 

 Math

 Science

 History

etc.....

I want to send(using post method) the selected categories(category[]) via mootools ajax so that if I dump the $_POST variable in the server I will get something like:

array(1) {
[category]=>
array(2) {
[0]=>
string(4) "Math"
[1]=>
string(7) "History"
}
}

What should be the javascript(mootools) code for it? Below is my partial code.

new Request.JSON({url: '/ajax_url',
            onSuccess: function(){
                alert('success');
            }
        }).post(???);

Note that I don't want to send first_name and last_name fields. I only want to send the category field which is an html array.

Find the answer here