Problem with instance of class while creating reusable controller in node.js

Question

I want to reuse all my servise and controllers and I was achieving this with extending class. I'm calling the class of Controller and service all the way up from a router. everything looks fine while creating instance of class, but when I send request to sign in route it says there is no this.servise or this.dto which is i passed to the constructor while creating this instance of object

import express from "express";
const router = express.Router();
import UserController from "../../controllers/user.controller";
import UserService from "../../services/user.service.js";
import {UserDto} from "../../dtos/user.dto.js";
import User from "../../models/User.js";

const userService = new UserService(User);
console.log(userService, UserDto);                             // successfully logged
const userController = new UserController(userService, UserDto);
console.log(userController);                                   // successfully logged
router.post('/signup', userController.signup);
router.post('/signin', userController.signIn);
router.post('/signout', userController.signOut);
router.get('/all', userController.getAll);

router.route("/:id")
    .get(userController.get)
    .post(userController.create)
    .patch(userController.update)
    .delete(userController.delete);

export default router;

export default class UserController extends MainController {
    async signIn(req, res) {
        try {
            const {email, password} = req.body;//await this.dto.login(req.body);
            const result = await this.service.signIn(email, password); // TypeError: Cannot read properties of undefined (reading 'service')
            return res.status(201).json({message: "successfully signed in", token: result.token, user: this.dto.output(result.user)});
        }
        catch(err){
            sendError(res, err);
        }
    }

I've reviewed my knowledge of how nodejs modules work, but I can't figure out what the problem is.

Who can explain me this situation, please!?

Thank you in advance!

You didn't define a constructor in UserController to set the field... — Trace
– Trace, Commented Nov 30, 2022 at 12:59
I did it MainController class and i did it too here with super when i tried to fix the issue, but it didn't help — Azim Umarov
– Azim Umarov, Commented Dec 1, 2022 at 10:43
Where is your call to super? I can't see it in your code (?). Perhaps also share the super class. — Trace
– Trace, Commented Dec 1, 2022 at 11:44
There's no need for a call to super if you don't have a constructor defined. I assume that MainController has an appropriate constructor... — Vladislav Zorov
– Vladislav Zorov, Commented Dec 1, 2022 at 16:52
yeah MainController has it. I just forget to bind, my question is answered thank you all for helping me guys! — Azim Umarov
– Azim Umarov, Commented Dec 2, 2022 at 12:06

Vladislav Zorov · Accepted Answer · 2022-12-01 16:39:15Z

1

You forgot to use .bind() when passing the references to the methods to the Express router. So who knows what the value of this will be when Express tries to call them (in JS, this doesn't work like other variable names, it doesn't use lexical scoping, what the value will be depends on the calling code).

Change your code to e.g.

router.post('/signup', userController.signup.bind(userController));

This will ensure that this is set to your userController object when the function gets called (bind() is a method available on all function objects that returns a new function with a fixed this value).

answered Dec 1, 2022 at 16:39

Vladislav Zorov

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3 Comments

Azim Umarov Over a year ago

yeah, thank you it works, do you any efficient idea for not repeating all binds

Vladislav Zorov Over a year ago

Not really :( personally I just don't do it like that, I don't use classes, just modules and normal functions... and since there's no "this" in them (just references to module-level variables), I also don't need "bind"...

Azim Umarov Over a year ago

Ok, thank you!. I was using modules too, but I like classes from other language :-)

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