Function iteratee

public/javascripts/async.js:447–456

(x, _, callback)

                if (cb) cb(getResult(false, void 0));
            }
            function iteratee(x, _, callback) {
                if (!cb) return callback();
                iterator(x, function (v) {
                    if (cb && check(v)) {
                        cb(getResult(true, x));
                        cb = iterator = false;
                    }
                    callback();
                });
            }
            if (arguments.length > 3) {
                eachfn(arr, limit, iteratee, done);
            } else {