code: function extend(filename, async) {
    if (async._waterfall !== undefined) {
      return;
    }
    async._waterfall = async.waterfall;
    async.waterfall = function (_tasks, callback) {
      let tasks = _tasks.map(function (t) {
        let fn = function () {
          console.log("async " + filename + ": " + t.name);
          t.apply(t, arguments);
        };
        return fn;
      });
      async._waterfall(tasks, callback);
    };
  }
docs: util to map async method names