Error handler npm

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• compression
• connect-rid
• cookie-parser
• cookie-session
• cors
• errorhandler
• method-override
• morgan
• multer
• response-time
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• serve-static
• session
• timeout
• vhost

Development-only error handler middleware.

This middleware is only intended to be used in a development environment, as
the full error stack traces and internal details of any object passed to this
module will be sent back to the client when an error occurs.

When an object is provided to Express as an error, this module will display
as much about this object as possible, and will do so by using content negotiation
for the response between HTML, JSON, and plain text.

• When the object is a standard Error object, the string provided by the
  stack property will be returned in HTML/text responses.
• When the object is a non-Error object, the result of
  util.inspect
  will be returned in HTML/text responses.
• For JSON responses, the result will be an object with all enumerable properties
  from the object in the response.

Install

This is a Node.js module available through the
npm registry. Installation is done using the
npm install command:

$ npm install errorhandler

API

var errorhandler = require('errorhandler')

errorhandler(options)

Create new middleware to handle errors and respond with content negotiation.

Options

Error handler accepts these properties in the options object.

log

Provide a function to be called with the error and a string representation of
the error. Can be used to write the error to any desired location, or set to
false to only send the error back in the response. Called as
log(err, str, req, res) where err is the Error object, str is a string
representation of the error, req is the request object and res is the
response object (note, this function is invoked after the response has been
written).

The default value for this option is true unless process.env.NODE_ENV === 'test'.

Possible values:

• true: Log errors using console.error(str).
• false: Only send the error back in the response.
• A function: pass the error to a function for handling.

Examples

Simple example

Basic example of adding this middleware as the error handler only in development
with connect (express also can be used in this example).

var connect = require('connect')
var errorhandler = require('errorhandler')

var app = connect()

if (process.env.NODE_ENV === 'development') {
  // only use in development
  app.use(errorhandler())
}

Custom output location

Sometimes you may want to output the errors to a different location than STDERR
during development, like a system notification, for example.

var connect = require('connect')
var errorhandler = require('errorhandler')
var notifier = require('node-notifier')

var app = connect()

if (process.env.NODE_ENV === 'development') {
  // only use in development
  app.use(errorhandler({ log: errorNotification }))
}

function errorNotification (err, str, req) {
  var title = 'Error in ' + req.method + ' ' + req.url

  notifier.notify({
    title: title,
    message: str
  })
}

License

MIT

throw Error('Error');

class SomethingIsWrongError extends Error {
  constructor() {
    super('Something is wrong!');
  }
}
throw new SomethingIsWrongError();

export class ErrorCode {
  public static readonly Unauthenticated = 'Unauthenticated';
  public static readonly NotFound = 'NotFound';
  public static readonly MaximumAllowedGrade = 'MaximumAllowedGrade';
  public static readonly AsyncError = 'AsyncError';
  public static readonly UnknownError = 'UnknownError';
}

export class ErrorModel {
  /**
   * Unique error code which identifies the error.
   */
  public code: string;
  /**
   * Status code of the error.
   */
  public status: number;
  /**
   * Any additional data that is required for translation.
   */
  public metaData?: any;
}

import { ErrorCode } from './error-code';

export class ErrorException extends Error {
  public status: number = null;
  public metaData: any = null;
  constructor(code: string = ErrorCode.UnknownError, metaData: any = null) {
    super(code);
    Object.setPrototypeOf(this, new.target.prototype);
    this.name = code;
    this.status = 500;
    this.metaData = metaData;
    switch (code) {
      case ErrorCode.Unauthenticated:
        this.status = 401;
        break;
      case ErrorCode.MaximumAllowedGrade:
        this.status = 400;
        break;
      case ErrorCode.AsyncError:
        this.status = 400;
        break;
      case ErrorCode.NotFound:
        this.status = 404;
        break;
      default:
        this.status = 500;
        break;
    }
  }
}

throw new ErrorException(ErrorCode.MaximumAllowedGrade, { max: 100 }); // object is optional

import { Request, Response, NextFunction } from 'express';
import { ErrorCode } from './error-code';
import { ErrorException } from './error-exception';
import { ErrorModel } from './error-model';

export const errorHandler = (err: Error, req: Request, res: Response, next: NextFunction) => {
  console.log('Error handling middleware called.');
  console.log('Path:', req.path);
  console.error('Error occured:', err);
  if (err instanceof ErrorException) {
    console.log('Error is known.');
    res.status(err.status).send(err);
  } else {
    // For unhandled errors.
    res.status(500).send({ code: ErrorCode.UnknownError, status: 500 } as ErrorModel);
  }
};

app.use(errorHandler); // registration of handler

app.listen(3000, () => {
  console.log('Application started on port 3000!');
});

app.get('/throw-unauthenticated', (req: Request, res: Response, next: NextFunction) => {
  throw new ErrorException(ErrorCode.Unauthenticated);
  // or
  // next(new ErrorException(ErrorCode.Unauthenticated))
});
app.get('/throw-maximum-allowed-grade', (req: Request, res: Response, next: NextFunction) => {
  throw new ErrorException(ErrorCode.MaximumAllowedGrade, { grade: Math.random() });
  // or
  // next(new ErrorException(ErrorCode.MaximumAllowedGrade, { grade: Math.random() }))
});
app.get('/throw-unknown-error', (req: Request, res: Response, next: NextFunction) => {
  const num: any = null;
  // Node.js will throw an error because there is no length property inside num variable
  console.log(num.length);
});

app.get('/', function (req, res) {
  throw new Error('BROKEN'); // Express will catch this on its own.
});

app.get('/', function (req, res, next) {
  fs.readFile('/file-does-not-exist', function (err, data) {
    if (err) {
      next(err); // Pass errors to Express.
    } else {
      res.send(data);
    }
  });
});

app.get('/user/:id', async function (req, res, next) {
  // if error appears in getUserById, express will automatically throw an error
  const user = await getUserById(req.params.id);
  res.send(user);
});

const someOtherFunction = () => {
  const myPromise = new Promise((resolve, reject) => {
    setTimeout(() => {
      reject(new ErrorException(ErrorCode.AsyncError));
    }, 1000);
  });
  return myPromise;
};
app.get('/throw-async-await-error', async (req: Request, res: Response, next: NextFunction) => {
  // express 4
  try {
    await someOtherFunction();
  } catch (err) {
    next(err);
    // next line will not work as expected
    // throw err
  }
  // express 5
  // await someOtherFunction();
});

GitHub Stars

410

Forks

60

Contributors

6

The npm package errorhandler receives a total of
1,187,440 downloads a week. As such, we scored
errorhandler popularity level to be Influential project.

Based on project statistics from the GitHub repository for the
npm package errorhandler, we found that it has been
starred 410 times.

Downloads are calculated as moving averages for a period of the last 12
months, excluding weekends and known missing data points.