Chaining Promises with JQuery in Javascript

so-many-promises.js

// Prereq: underscore.js and jquery loaded

var p1 = $.Deferred();
var p2 = $.Deferred();

// We want something that chains promises, so something like...
//p1.done(
//    function addNext() {
//        p2.done(
//            function addNext() {
//                console.log('oh hai');
//            }
//        )
//    }
//);

function chainPromise( promiseList, successCallback, failCallback ) {
    var hasFailed = false;

    // When all promises resolve, call successCallback();
    var resolver = _.reduce(
        promiseList,
        function iterator(memo, promise) {
            return function addNext() {
                if ( !hasFailed ) {
                    promise.done(memo);
                }
            };
        },
        successCallback
    );
    resolver();

    // If any promise fails, call failCallback, and only call it once();
    _.each(
        promiseList,
        function iterator(promise) {
            promise.fail(
                function onFail() {
                    if ( !hasFailed ) {
                        hasFailed = true;
                        failCallback();
                    }
                }
            )
        }
    );
}

chainPromise( [p1, p2],
    function() { console.log('oh hai'); },
    function() { console.log('oh noes'); }
);

console.log('loaded with promises');
p1.resolve();
console.log('almost there');
p2.resolve();

//console.log('rejected...');
//p2.reject();
//p1.reject();