Function done

public/javascripts/async.js:238–248

(err)

        if (completed === 0) callback(null);

        function done(err) {
            completed--;
            if (err) {
                callback(err);
            }
            // Check key is null in case iterator isn't exhausted
            // and done resolved synchronously.
            else if (key === null && completed <= 0) {
                callback(null);
            }
        }
    };

    async.forEachOfSeries =