Dynamic Error Handler

A clean, modular, and dynamic Express error handler middleware with centralized logging and custom error class — written in TypeScript. Handles common errors like CastError, ValidationError, MongoDB duplicates, JWT errors, and more.

Features

• ✅ Custom AppError class for operational errors
• ✅ Dynamic error handler middleware with extensible error handling
• ✅ catchAsync helper to wrap async route handlers and forward errors
• ✅ Centralized error logging to logs/error.log (configurable)
• ✅ Clear JSON error responses for both development and production
• ✅ Toggle detailed logging with a simple flag
• ✅ TypeScript-ready

Installation

npm install dynamic-error-handler

Usage

Basic Setup

import express from "express";
import {
  AppError,
  createErrorHandler,
  catchAsync,
} from "dynamic-error-handler";

const app = express();

app.get(
  "/test",
  catchAsync(async (req, res, next) => {
    // Simulate an async error
    return next(new AppError("Something went wrong!", 400));
  })
);

// Use the error handler middleware after all routes
app.use(
  createErrorHandler({
    logErrors: true,
    MyCustomError: (err: any) =>
      new AppError(`Custom error: ${err.message}`, 400),
  })
);

app.listen(3000, () => {
  console.log("Server running on port 3000");
});

API

AppError

Custom error class extending the built-in Error class.

new AppError(message: string, statusCode?: number)

• message: Error message string
• statusCode: HTTP status code (default: 400)

catchAsync

Wrap your async route handlers to automatically catch errors and forward them to the error handler.

const catchAsync =
  (fn: (req: Request, res: Response, next: NextFunction) => Promise<any>) =>
  (req, res, next) => {
    fn(req, res, next).catch(next);
  };

createErrorHandler(options?)

Express error handling middleware. Use at the end of your middleware stack.

• options (optional):

  • logErrors (boolean): If true, errors are logged to logs/error.log and console (default: false).

Example:

app.use(createErrorHandler({ logErrors: true }));

Supported Error Types

• CastError (Mongoose invalid IDs)
• ValidationError (Mongoose validation)
• MongoDB duplicate key errors
• JWT errors (JsonWebTokenError, TokenExpiredError)
• Other unknown errors are handled gracefully

Logging

• Logs are appended to logs/error.log in your project root.
• If logErrors option is enabled, errors are printed to console and saved in the log file.
• If disabled, logging is suppressed.

Development & Production Modes

• In development mode (NODE_ENV=development), full error stack and details are sent in JSON response.
• In production mode, only trusted operational errors show details; otherwise, a generic message is sent.

License

MIT © Ankit Kumar

Contribution

Feel free to open issues or submit pull requests!

Acknowledgments

Inspired by best practices in Express error handling and TypeScript utilities.