How to write typescript method to replicate javascript method

Question

I have this code in javascript:

// find the user
  User.findOne({
    name: req.body.name
  }, function(err, user) {

    if (err) throw err;

    if (!user) {
      res.json({ success: false, message: 'Authentication failed. User not found.' });
    } else if (user) {

            //issue token
        }

    })

User.findOne coming for mongoose. But I want to mock that method so I won't talk to database at this point. But want to keep the logic like it is so I need to write my own User.findOne typescript analogue so is behave same.

That is what I come up so far:

export class User { 

    constructor() { }

    public findOne(user: any, next:Function) {
        console.log(1); //getting there
        var fake = {name: "a", password: "p"};

        return fake;
    }
}

and I am importing my code like that

import {User} from '../mock/User'; 

     var login = {name: req.body.name, password: req.body.password} //fake   

     // find the user
      User.prototype.findOne({
        user: login
      }, function(err, user) {
      console.log(2); //not getting there when using my User.findOne from .ts
      ........
}

But code that followed by function(err, user) just not getting executed.

Do you have any ideas how to fix that?

UPDATE: Just tried to use lambdas but still same issue:

User.findOne({user: login}, (err, user) => {
   console.log("test"); //- this code inside function just not executed
})

Answer 1

If you want the method to be called directly from the User class and not from an instance you need to declare it as static.

public static findOne(user: any, next:Function) {
        console.log(1); //getting there
        var fake = {name: "a", password: "p"};
        next(undefined,fake); //this will call the function you passed as lambda or regular function
}

This way you can call the method like this.

User.findOne({},(error,result)=>{
   //using a lambda here to make sure you have no issues with 'this' but you can also pass a regular function object.
  console.log(result);
  console.log(error);
}

Answer 2

Try defining at user.ts a class named User with an static method named findOne(err, user):

user.ts

export class User {

  constructor(){}

  static findOne(query, user: Function) {
    // whatever
  }
}

use it as:

import * as User from './path/user'

User.findOne({...}, (err, user) => {
   // whatever
})

Apart, a tip which I find so useful: use typescript to define the signature of your callback instead of just Function, defining the arguments of your cb; for example:

user.ts

export class User {

  // callback function has 2 arguments: err and user (you can specify their types too
  static findOne(query: any, cb: (err: any, user: any) => void) {
    // whatever
  }
}