Function _concat

examples/browser/nodeunit.js:1003–1013

(eachfn, arr, fn, callback)

    };

    var _concat = function (eachfn, arr, fn, callback) {
        var r = [];
        eachfn(arr, function (x, cb) {
            fn(x, function (err, y) {
                r = r.concat(y || []);
                cb(err);
            });
        }, function (err) {
            callback(err, r);
        });
    };
    async.concat = doParallel(_concat);
    async.concatSeries = doSeries(_concat);