code: function async(){
      console.log('================ async start ================');
      var deferred = Promise.defer();
      var app = new App('async');
      app.syncMethod(0, function(error, ret){
          console.log(ret);
          console.log('--------------------------');
          app.asyncMethod1(1, function(error, ret){
              console.log(ret);
              console.log('================ async end ================');
              console.log('');
              deferred.resolve();
          });
      });
      return deferred.promise;
  }
docs: async callback