Request queue for JavaScript

requestQueue.js

function requestQueue(url, startCallback, doneCallback) {
    var requests = [];

    function createRequest(parameters) {
        var f = function() {
            $.post(url, parameters)
		            .done(function() {
		                if (requests.length > 0) {
		                    //console.log("processing next request");
		                    var next = requests.pop();
		                    next();
		                } else {
		                    //console.log("done");
		                    doneCallback();
		                }
		            });
        };

        return f;
    }

    function enqueue(parameters) {
        requests.push(createRequest(parameters));
    }

    function start() {
        var first = requests.pop();
        if (first == undefined) {
            //console.log("empty queue");            
        } else {
            //console.log("starting");
            startCallback();
            first();
        }
    }

    return {
        start: start,
        enqueue: enqueue
    };
}

So every time you call requestQueue, what type of function would startCallback, doneCallback be? Can you provide an example to give some context as to how you call it? Thanks...
is it something like this perhaps?
var finished = false;
var p1 = requestQueue(url. p1.start, p2)
var p2 = requestQueue(url, p2.start, completed)
function completed() (
finished = true;
)