async.js return last value when use waterfall method

Question

all. I'm using asyncjs's waterflow method to return res value at last.But following code is return undefined value.

var async = require("async");
User.findBy = function(name,password){
  async.waterfall([
      function fetch(callback){
        db.lrange("users",0,-1,function(err,users){
          users.forEach(function(item){
            var u = JSON.parse(item);
            if ((u.name == name) && (u.password == password)){
              console.log(u);
              callback(null,u);
              return;
            }
          });
        });
        callback(null);
      }
      ],function end(err,res){

        setTimeout(function(){
        // I want to return res value at last.
        return u;
        },0);
      });
};

app.js

 // but it returns undefined value.
 var user = User.findBy("nobinobiru",a");

Do you have any idea? Please any help. Thanks in advance.

I don't know asyncjs, but it sounds like you're trying to get the result synchronously (that's what var user = and return imply). Is that what you're trying to do? — pimvdb
– pimvdb, Commented Aug 4, 2012 at 11:44
The User.findBy doesn't have return statement so its return value is undefined. Make it take a callback and call that. — Esailija
– Esailija, Commented Aug 4, 2012 at 11:48
You can't do what you're trying to do the way you're trying to do it. Also, using "waterfall" when you've just got one function to call seems unnecessary. — Pointy
– Pointy, Commented Aug 4, 2012 at 11:50

Vadim Baryshev · Accepted Answer · 2012-08-04 13:33:31Z

In fetch function you calling callback(null); immediately after the db.lrange call. This call unnecessary here, because you need to wait results from db.

This code should work fine:

var async = require("async");
User.findBy = function(name,password){
    async.waterfall([
        function fetch(callback){
            db.lrange("users",0,-1,function(err,users){
                var user;
                if (users && users.length) {
                    users.forEach(function(item){
                        var u = JSON.parse(item);
                        if ((u.name == name) && (u.password == password)){
                            console.log(u);
                            user = u;
                            return;
                        }
                    });
                    callback(null,user);
                } else {
                    callback(null);
                }
            });
        }
    ],function end(err,res){

        setTimeout(function(){
            // I want to return res value at last.
            return res;
        },0);
    });
};

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