Non riesco a capire il funzionamento di questo script

            var timer = function timer(delay) {
                var whenTimedOut = $.Deferred(),
                        promise = whenTimedOut.promise();
                promise.cancel = function (payload) {
                    whenTimedOut.reject(payload);
                };
                setTimeout(function () {
                    whenTimedOut.resolve();
                }, delay);
                return promise;
            };
            asyncTest('Deferred', function () {
                var startTime = new Date(),
                        delay = 30,
                        afterTimeout = 50,
                        cancelTime = 100,
                        myTimer = timer(delay),
                        cancelTimer = timer(cancelTime);
                expect(4);
                myTimer.done(function () {
                    ok(true,
                            'First callback fired.');
                });
                myTimer.done(function () {
                    var now = new Date();
                    ok((now - startTime) > delay,
                            'Delay works.'
                            );
                });
                setTimeout(function () {
                    ok(true,
                            'Fires after timeout expires.');
                }, afterTimeout);
                setTimeout(function () {
                    start();
                }, afterTimeout + 20);
                cancelTimer
                        .done(function () {
                            ok(false,
                                    'A canceled timer should NOT run .done().');
                        })
                        .fail(function () {
                            ok(true,
                                    'A canceled timer calls .fail().');
                        })
                        .cancel();
            });