create-node-mongo-express-app/bin/template/src/middleware/errorhandler.middleware.ts

Node Js Template with MVC pattern, typescript, mongoose and express

import mongoose from 'mongoose';
import logger from '../utils/winston.logger';

import { NextFunction, Request, Response } from 'express';
import { ApiError } from '../utils/ApiError';

interface CustomError extends Error {
  statusCode?: number;
  errors?: never[]; // For Mongoose validation errors
}

const errorHandler = (
  err: CustomError | ApiError<Error>,
  req: Request,
  res: Response, //eslint-disable-next-line @typescript-eslint/no-unused-vars
  next: NextFunction,
) => {
  let error = err;

  // Check if the error is an instance of an ApiError class which extends native Error class
  if (!(error instanceof ApiError)) {
    // if not
    // create a new ApiError instance to keep the consistency

    // assign an appropriate status code
    const statusCode =
      error.statusCode || error instanceof mongoose.Error ? 400 : 500;

    // set a message from native Error instance or a custom one
    const message = error.message || 'Something went wrong';
    error = new ApiError(statusCode, message, error?.errors || [], err.stack);
  }

  // Now we are sure that the `error` variable will be an instance of ApiError class
  const response = {
    ...error,
    message: error.message,
    ...(process.env.NODE_ENV === 'development' ? { stack: error.stack } : {}), // Error stack traces should be visible in development for debugging
  };

  logger.error(`${error.message}`);

  // Send error response
  return res.status(error.statusCode).json(response);
};

export { errorHandler };