An asynchronous for each series runner. Feed this a contiguous array of functions that accept a single (callback([error])) argument.

asyncForEachSeries.js

// Simple asynchronous forEach.
function forEachSeries(list, func, callback) {
    var listIndex = 0;

    function doOne(err) {
        if (err) {
            return callback(err);
        }

        var thisElem = list[listIndex];

        if (!thisElem) {
            return callback();
        }

        listIndex += 1;

        func(thisElem, doOne);
    }

    doOne();
}

Updated to avoid array slicing.