when you assign functions to variables without the var keyword they either overwrite the local variable of that name or the are added to the global namespace. (so your do_stuff is a global function, which is not what you want)

one way to do what you want is to explicitly give where you want your function to reside.

(function($) { 

    $.fn.foo = function(options) {

        // whatever $().foo() should do

    };



    $.fn.foo.do_stuff = function() {

        console.log(hello world!);

    };



    $.fn.foo.do_stuff.do_other_stuff = function(){

        alert(who are you?);

    };

})(jQuery);

Edit:

This works because all functions in javascript are objects, which means you can assign values to any arbitrary property.

If you want to access the variables of other functions you can move the definitions inside of the other ones like:

$.fn.foo.do_stuff = function() {

    console.log(hello world!);

    $.fn.foo.do_stuff.do_other_stuff = function(){

        alert(who are you?);

    };

};

but this will mean the function is only defined once you run the other function, and that each time you run the function it will overwrite the last definition.

Possibly a more ideal solution would be to have each function return an object containing the nested function like so:

(function($) { 

    $.fn.foo = function(options) {

        // whatever $().foo() should do



        var do_stuff = function(do_stuff_args) {

            console.log(hello world!);

            // do stuff with options and do_stuff_args



            var do_other_stuff = function(other_args) {

                alert(who are you?);

                // here you have access to options, do_stuff_args, and other_args

            };



            return {

                do_other_stuff: do_other_stuff

            };

        };



        return {

            do_stuff: do_stuff

        }

    };

})(jQuery);

and call it using

foo().do_stuff(some_options).do_other_stuff(other_options);

or

var a = foo(stuff).do_stuff(some_options);

a.do_other_stuff(foo);

a.do_other_stuff(bar);