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')

installation

npm install extend-error

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

syntax

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

polyfilling

All of the examples here assume you ran polyfill(). If you're not comfortable with modifying native objects, you can use extendError() directly.

var extendError = require('extend-error');
var ClientError = extendError('ClientError', 400);
var HttpNotFound = extendError(ClientError, HttpNotFound, 404);

more examples for a web app

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');

instanceof

throw an error in controller

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

throw err;
(or)
callback(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');
    log.error(err);
}