Easily define custom error types in Node.js

Usage no npm install needed!

<script type="module">
  import extendError from 'https://cdn.skypack.dev/extend-error';



Ever tried to create custom error types in Node.js and wished it should be this simple?

var MyError = Error.extend('MyError');
throw MyError('wow')


npm install extend-error

and in your app.js, just require('extend-error'). It will provide you an extend() method for the Error type.


  • extend() takes two arguments : subTypeName & errorCode [optional]
  • it returns the newly created error type

more examples for a web app

something useful

var AppError = Error.extend('AppError', 500);
var ClientError = Error.extend('ClientError', 400);

extend ClientError further for specific http types

var HttpNotFound = ClientError.extend('HttpNotFoundError', 404);
var HttpUnauthorized = ClientError.extend('HttpUnauthorized', 401);

throwing errors

throw new AppError('unable to connect db due to error: ' + err);

throw new ClientError({'message':'required field missing', field: 'email'})

throw new HttpNotFound('no post found with id: ' + id);

throw new HttpNotFound({'message': 'no such post', 'id': id});

don't worry when you forget 'new'

throw ClientError('bad request');


throw an error in controller

var err = HttpNotFound('user profile not found');

throw err; 

handle it easily in global error handler (in case of express.js error middleware)

if (err instanceof ClientError) {
    //send out the actual message
    res.send(err.code, err.message);
} else {
    //send out a generic message
    res.send(500, 'oops! something went wrong');