CODEWITHSUNDEEP
javascriptnode.jsexpress
nodejsnoob
nodejsnoob

Reputation: 43

Cannot access class properties inside a method

I started learning node.js and I am currently struggling with my middleware I wrote in node.js. It should be an Error handler. The problem is that I cannot access properties I defined inside constructor method. I get this error:

TypeError: Cannot read property 'response' of undefined notFound(/[irrelevant]/src/middleware/ErrorHandler.js:12:8)

This is my code:

ErrorHandler.js

class ErrorHandler {
    
    constructor() {
        this.response = {
            success: false,
            errorMessage: '',
            status: 0
        }
    }

    notFound(req, res, next) {
        this.response.errorMessage = 'Not Found'
        this.response.status = 404
        res.status(404).send(this.response)
    }
    
    badRequest(req, res, next) {
        this.response.errorMessage = 'Bad request'
        this.response.status = 400
        res.status(400).send(this.response)
    }
    
}

module.exports = new ErrorHandler()

routes.api.js

// Import modules
const express = require('express')
const router = express.Router()

// Import controller
const contactController = require('../controllers/ContactController')

// Import error handler
const errorHandler = require('../middleware/ErrorHandler')

router.post('/contact', contactController.index)

// return 404 if no matching routes were found
router.use(errorHandler.notFound)

module.exports = router

maybe the code doesn't make any sense, I just need the answer what is causing the error, It's not the code for production purposes.

thank you in advance and have a nice day

Upvotes: 4

Views: 2633

Answers (2)

Gogu Gogugogu
Gogu Gogugogu

Reputation: 332

Define your methods like this:

notFound = (req, res, next) => {}

Upvotes: 10

Tushar Shahi
Tushar Shahi

Reputation: 20441

You are passing in a function errorHandler.notFound to the middleware. Next time it is called, it will not be bound to the object you exported.

So this will not be your new ErrorHandler(). In case you want to achieve that you can do two things: bind the method to the this in the constructor.

Or use arrow function as mentioned by @Gogu. Arrow functions take this from their surroundings where they are defined.

Upvotes: 5

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