failure

Failure is a small helper library which allows you to easily generate custom error objects which can hold addition properties which could be helpful for debugging your application. In addition to that, it automatically adds a missing toJSON function to the Error object so you can actually get the message and stack trace once you JSON.stringify the error instance.

Installation

The module is written with browsers and servers in mind and should run in any environment that runs ES3. The module it self is released in the public npm registry and can be installed using:

npm install --save failure

The --save flag tells npm to automatically add the installed version to your package.json file as new dependency.

Usage

First of all, start with including this module in your code:

'use strict';

var failure = require('failure');

Now every time you want to pass or create a new Error instance, you can use the failure function to generate the error for you. The failure method accepts 2 arguments:

1. An Error instance that just needs extra props, or a string that should be transformed to an Error. Please do note that when using a string you will have an extra trace in your stack trace as the stack trace will be made inside the failure function instead of where you called the failure function.
2. An object with extra properties that should be introduced on the supplied or generated Error instance. These properties will not override existing properties on the Error instance.

Before the function returns the generated Error instance it checks if it also needs to add the missing .toJSON method.

Below is a small usage example on how you could use this to provide extra information when things start failing when you make an HTTP request somewhere. If request something with an incorrect status code, you might want to know what statusCode was received, so we can easily add that to the Error object. Same as parse errors for JSON, you probably want to know what you received and failed.

request('https://googlllll.com', function (err, res, body) {
  if (err) return next(err);
  if (res.statusCode !== 200) return next(failure('Invalid statusCode'), {
    statusCode: res.statusCode
  });

  try { body = JSON.parse(body); }
  catch (e) {
    return next(failure(e, { 
      body: body 
    }));
  }

  next(undefined, body);
})

License

MIT