Class methods in node.js

Question

I've been trying for the last hour to write a user module for passport.js with the findOne, findOneOrCreate, etc. methods, but can't get it right.

User.js

var User = function(db) {
  this.db = db;
}

User.prototype.findOne(email, password, fn) {
  // some code here
}

module.exports = exports = User;

app.js

User = require('./lib/User')(db);
User.findOne(email, pw, callback);

I've been through dozens of errors, mostly

TypeError: object is not a function

or

TypeError: Object function () {
  function User(db) {
    console.log(db);
  }
} has no method 'findOne'

How do I create a proper module with these functions without creating an object/instance of User?

Update

I went over the proposed solutions:

var db;
function User(db) {
  this.db = db;
}
User.prototype.init = function(db) {
  return new User(db);
}
User.prototype.findOne = function(profile, fn) {}
module.exports = User;

No luck.

TypeError: Object function User(db) {
  this.db = db;
} has no method 'init'

Solution 1

A couple of things are going on here, I've corrected your source code and added comments to explain along the way:

lib/User.js

// much more concise declaration
function User(db) {
    this.db = db;
}

// You need to assign a new function here
User.prototype.findOne = function (email, password, fn) {
    // some code here
}

// no need to overwrite `exports` ... since you're replacing `module.exports` itself
module.exports = User;

app.js

// don't forget `var`
// also don't call the require as a function, it's the class "declaration" you use to create new instances
var User = require('./lib/User');

// create a new instance of the user "class"
var user = new User(db);

// call findOne as an instance method
user.findOne(email, pw, callback);

Solution 2

You need to new User(db) at some point.

You could make an init method

exports.init = function(db){
  return new User(db)
}

And then from your code:

var User = require(...).init(db);

Comments

[Bryan]

In case it helps, see the answer in stackoverflow.com/questions/39932009/node-express-middleware‌​/… that shows how to create an Express middleware function that has access to class methods. This answer assumes ES6 class is available.

[Robert K]

Yes, technically he's just imported the class reference... not instantiated it.

[Patrick]

Hm, ok. I was hoping I'll get around an instance. This seems to be the nicest solution. Thanks!

[3on]

You are welcome. Java people call that a factory if I'm not mistaken.

[Patrick]

Jepp, I went through all the patterns. It seems that some libraries do it without instance though. I updated the question, the solution doesn't quite work yet.

[3on]

Well you do not have to do "classes" that you new you can just have a modular approach if you do not need multiple instance of you that particular code. by having only exports.myFunction = function() {...}. Beside you did not get my first solution.

[Patrick]

Ok, got it working now! I thought I still need the module.exports.

[3on]

You don't want to export the "class" you just want to exports the module method which returns you an Object User on which you have define some method in the its prototype.