promise-loop-sequence.js

var urlList = model.getURLs();

var loadAndParse = function (url)
{
	// both load() and parse() are promise based functions
	return load(url).then(parse);
};

/**
 * Allows for the sequentially calling of promise based functions by iterating over a list of
 * items and then calling the next promise based function when the previous one has resolved.
 *
 * @param {array} arr List of values or objects used to pass into the promise-based `iterator`
 * parameter function.
 * @param {function} iterator The promise-based function to call with an item from the `arr` parameter.
 * @returns {promise}
 */
var promiseLoopSequence = function (arr, iterator)
{
	// create a empty promise to start our series (so we can use `then`)
	// we save Q to qPromise so JSLint doesn't complain about no "new" keyword
	var qPromise = Q;
	var currentPromise = qPromise();
	var promises = arr.map(function (el)
	{
		return currentPromise = currentPromise.then(function ()
		{
			// execute the next function after the previous has resolved successfully
			return iterator(el);
		});
	});
	// group the results and return the group promise
	return Q.all(promises);
};

return promiseLoopSequence(urlList, loadAndParse);