Using a module for my DB, I am not retrieving my data

Question

Sorry if the title is not quite descriptive.

I am using Node and trying to use export.module to have clean code.

app.js

// ...
require('./router')(app);
module.exports = app;

router.js

cloudant = require("./helpers/cloudant")
// ...
module.exports = (app) => {
// ...
 app.post("/statsPage", function(req, res) {
 // ... 
  var a = cloudant.listUsers();
  console.log("from post ", a) // --> it shows ("undefined")
  if(a == false || a == undefined ) {
    res.render("error");
  } else {
    res.render("statsPage", {
      results: a
  });
}

cloudant.js

exports = module.exports = {}

exports.listUsers = function() {
 db.find({selector: {_id:{ "$gt": 0}}}, function(err, body) {
  if(err) {
   console.log(err);
   return false;
  } else {
   console.log(body.docs) // --> it shows results correctly
   return body.docs;
  }
 });
}

I've made the same way others "export" methods, like "insert", so I'm convinced that this issue is not related neither to my db connection or export "config".

Answer 1

The db.find method is asynchronous, so the data you get from the database is only available in the callback function. If you look carefully at the function you're exporting in cloudant.js, you'll see that there is no return statement returning any data, only in the callback function, that doesn't help anything.

There are many ways to solve this (and many, many posts on SO dealing with it).

Simplest solution for you would be to pass your own callback to your listUsers function:

exports.listUsers = function (callback) {
    db.find({ selector: { _id: { "$gt": 0 } } }, function (err, body) {
        if (err) {
            console.log(err);
            callback(err);
        } else {
            callback(body.docs);
        }
    });
}

router.js

app.post("/statsPage", function(req, res) {
    cloudant.listUsers(function (a) {
        console.log("from post ", a);
    });
});