Node.js custom error handling

Question

I am working on an application. In that application I am defining some custom error like below

'use strict';

/**
 * Validation error.
 * The Default HTTP STATUS CODE for ValidationError is 400 (HTTP BAD REQUEST)
 *
 */

/* Globals */
var HTTP_BAD_REQUEST = 400;
var NAME = 'ValidationError';

/**
 * Constructor
 *
 * @param {String}      message       The validation error message
 */
function ValidationError(message) {
  this.name = NAME;
  this.message = message;
  this.code = HTTP_BAD_REQUEST;
}

ValidationError.prototype = new Error();

/**
 * Module exports
 */
module.exports = ValidationError;

Now I use require to import this module in other modules like

var UnauthorizedError = require('../errors/UnauthorizedError')

In controller

// perform some logic
if(somecondition) {
    // call global error handler
    next(new ValidationError('id is must');
} else {
    // call next middleware
    next();
}

Enen if somecondition is false next() is calling error handler middleware.

I defined my error handler middleware like below

var winston = require('winston');
var HTTP_INTERNAL_SERVER_ERROR = 500;
var MESSAGE = 'Internal Server Error';

/**
 * Express standard error middleware
 *
 * @param  {Error}      err     error object
 * @param  {Object}     req     express request object
 * @param  {Object}     res     express response object
 * @param  {Function}   next    express next function
 */
var middleware = function(err, req, res) {
  winston.error(err);
  res.status(err.code || HTTP_INTERNAL_SERVER_ERROR).json(err.message || MESSAGE);
};

/**
 * Module exports
 */
module.exports = function() {
  return middleware;
};

I use errorHandler in my app like

app.use(errorHandler());

NOTICE that in error handler I am sending json data to client with some status code and error message. But if I check in postman the response headers are

Connection → keep-alive
Content-Length → 695
Content-Type → text/html; charset=utf-8
Date → Thu, 22 Jan 2015 14:18:13 GMT
X-Content-Type-Options → nosniff
X-Powered-By → Express

The content body is stack trace of error I have verified that next with error is not called and somecondition is false and error Handler middleware is also not called.

can you post the rest of your middleware scaffolding?

Paul
– Paul

2015-01-22 14:52:00 +00:00
Commented Jan 22, 2015 at 14:52 — Paul
– Paul, Commented Jan 22, 2015 at 14:52

Syed · Accepted Answer · 2015-01-22 18:18:22Z

3

I don't want to answer my own question. But for the sake of community I am posting it. I hope it will be useful to anyone.

The below middleware declaration

var middleware = function(err, req, res) {
  winston.error(err);
  res.status(err.code || HTTP_INTERNAL_SERVER_ERROR).json(err.message || MESSAGE);
};

Error middleware should accept 4 arguments.

answered Jan 22, 2015 at 18:18

Syed

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