Custom error response not working in nodejs written in typescript

Question

I have a custom general error response and it will run when execute return next(error), but it's not working , it threw an error to the console. Please help me and give me an explanation for this.

useErrorHandler.ts: This is my custom error response extending Error

import { Request, Response } from 'express';

export class ErrorResponse extends Error {
  public statusCode: number;

  constructor(message: string, statusCode: number) {
    super(message);
    this.statusCode = statusCode;
  }
}

const handleError = (err: any, req: Request, res: Response) => {
  res.status(err.statusCode || 500).json({
    success: false,
    error: err.message || 'Internal Server Error',
  });
};

export default handleError;

category.controller.ts: This is my controller, i tried to give an error

import { NextFunction, Request, Response } from 'express';
import { createCategory } from '../services/category.service';
import { ErrorResponse } from '../middlewares/error';

export const handleCreateCategory = async (
  req: Request,
  res: Response,
  next: NextFunction
) => {
  // const category = await createCategory(req.body);
  // return res.status(200).send(category);
  return next(new ErrorResponse('cccca 3000', 401));
};

app.ts: this is my main file, it contains routes, headers, middlewares, etc.

import express, { Express, Response, Request } from 'express';
import {
  authRouter,
  productRouter,
  categoryRouter,
  cartRouter,
} from './routes';
import { useErrorHandler } from './middlewares';

class App {
  public express: Express;
  private readonly ENDPOINT: string;

  constructor() {
    this.express = express();
    this.ENDPOINT = '/api/v1';
    this.setHeaders();
    this.setMiddlewares();
    this.mountRoutes();
  }

  private setHeaders(): void {}

  private setMiddlewares(): void {
    this.express.use(express.json());
    this.express.use(express.urlencoded());
  }

  private mountRoutes(): void {
    this.express.use(`${this.ENDPOINT}/auth`, authRouter);
    this.express.use(`${this.ENDPOINT}/product`, productRouter);
    this.express.use(`${this.ENDPOINT}/category`, categoryRouter);
    this.express.use(`${this.ENDPOINT}/cart`, cartRouter);

    //handle err
    this.express.use(useErrorHandler);
  }
}

export default new App().express;

Using Postman to test the error response

The handleError function must have 4 arguments that is how express recognise it as an error handler. Docs ... error-handling functions have four arguments instead of three: (err, req, res, next). — Molda
– Molda, Commented Sep 3, 2021 at 6:04

Lucas Fabre · Accepted Answer · 2021-09-03 10:15:44Z

1

Your error-handler middleware should always have 4 arguments. That's how Express knows it is an error-handler method.

If you write your handleError function like the code below it will work.

const handleError = (err: any, req: Request, res: Response, next: NextFunction) => {
  ...
};

You can read more about it in the official Express Docs.
https://expressjs.com/en/guide/error-handling.html

Refer to the section Writing error handlers.

edited Sep 3, 2021 at 10:15

answered Sep 3, 2021 at 10:09

Lucas Fabre

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