Waterfall stolen from async-waterfall with multi-environment boilerplate removed

Example

waterfall([
		function createBasket(cb) {
			api.Basket().create({ artistid: 1 }, function processReleases(err, res) {
				if (err) { return cb(err); }
				basketId = res.basket.id;
				console.log('Created basket', basketId);
				return cb();
			});
		},
		function addToBasket(cb) {
			api.Basket().addItem({
				basketId: basketId,
				releaseId: 769006,
				trackId: 13166687 // Test content
			}, function (err, res) {
				if (err) { return cb(err); }
				console.log('Added to basket: ', res.basket.basketItems[0]);
				return cb();
			});
		},
		function applyVoucher(cb) {
			api.Basket().applyVoucher({
				basketId: basketId,
				voucherCode: voucherCode
			}, function (err, res) {
				if (err) { return cb(err); }
				console.log('Applied voucher to: ', res.basket.basketItems[0]);
				return cb();
			});
		}
], function (err) {
	if (err) { throw err; }
	console.log('Example completed successfully');
});

Implementation

var makeIterator = function (tasks) {
	var makeCallback = function (index) {
		var fn = function () {
			if (tasks.length) {
				tasks[index].apply(null, arguments);
			}
			return fn.next();
		};
		fn.next = function () {
			return (index < tasks.length - 1) ? makeCallback(index + 1): null;
		};
		return fn;
	};
	return makeCallback(0);
};

var waterfall = function (tasks, callback) {
	callback = callback || function () {};
	if (!Array.isArray(tasks)) {
		var err = new Error('First argument to waterfall must be an array of functions');
		return callback(err);
	}
	if (!tasks.length) {
		return callback();
	}
	var wrapIterator = function (iterator) {
		return function (err) {
			if (err) {
				callback.apply(null, arguments);
				callback = function () {};
			} else {
				var args = Array.prototype.slice.call(arguments, 1);
				var next = iterator.next();
				if (next) {
					args.push(wrapIterator(next));
				} else {
					args.push(callback);
				}
				setImmediate(function () {
						iterator.apply(null, args);
						});
			}
		};
	};
	wrapIterator(makeIterator(tasks))();
};