standard-http-error

StandardHttpError.js

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StandardHttpError.js is a very simple but useful error class for JavaScript and Node.js that represents HTTP errors. You can then detect it with instanceof in error handling middleware and act accordingly.

You can use StandardHttpError.js with any error code you like, standardized or not. They don't have to exist beforehand, so if you're living on the cutting edge, feel free to use new HttpError(451, "Unavailable For Legal Reasons").

Installing

npm install standard-http-error

StandardHttpError.js follows semantic versioning, so feel free to depend on its major version with something like >= 1.0.0 < 2 (a.k.a ^1.0.0).

Using

var HttpError = require("standard-http-error")
throw new HttpError(404)

Your error handler will then receive an instance of HttpError along with the following enumerable properties:

Property	Value
name	"HttpError"
code	404
message	"Not Found"

As always for errors, the non-enumerable stack property is there as well.

For compatibility with Express or Koa's default request handler (the one that prints your errors out if you don't handle them), StandardHttpError.js also sets status, statusCode and statusMessage to be aliases of code and message. They're non-enumerable to not pollute serialization.

Creating a new instance by error name

StandardHttpError.js also supports passing a constant name instead of the error code. Constant names are taken from Node.js's Http module's STATUS_CODES object so they'll always be up to date.

new HttpError("NOT_FOUND")
new HttpError("FORBIDDEN")

See below for a list of error code names.

Setting a custom message

new HttpError(412, "Bad CSRF Token")

The default "Precondition Failed" message that the error code 412 would've resulted in will then be replaced by "Bad CSRF Token".

Note that status messages were always meant to be human readable, so it's perfect fine and even preferable to provide clarification in the status message. Try to stick to the capitalized form, though, as that will match the default HTTP status message style.

Setting custom properties

You can pass custom properties to be attached to the error instance as an object:

new HttpError(404, {url: req.url})
new HttpError(412, "Bad CSRF Token", {session: req.session})

You can access the given session property then as err.session.

Subclassing StandardHttpError

If you wish to add your own functionality to StandardHttpError, subclass it:

var HttpError = require("standard-http-error")

function RemoteError(res) {
  HttpError.call(this, res.statusCode, res.statusMessage)
}

RemoteError.prototype = Object.create(HttpError.prototype, {
  constructor: {value: RemoteError, configurable: true, writeable: true}
})

The StandardError.js library that StandardHttpError.js uses makes sure the name and stack properties of your new error class are set properly.

If you don't want your new error class to directly inherit from StandardHttpError, feel free to leave the RemoteError.prototype line out. Everything will work as before except your RemoteError will no longer be an instanceof StandardHttpError.js. You might want to manually grab the HttpError.prototype.toString function then though, as that's useful for nice String(err) output.

Switching based on error codes

switch (err.code) {
  case HttpError.UNAUTHORIZED: return void res.redirect("/signin")
  case HttpError.NOT_FOUND: return void res.render("404")
  case 451: return void res.redirect("/legal")
  default: return void res.render("500")
}

Using with Express

StandardHttpError.js comes very handy when used with Connect/Express's error handling functionality:

var HttpError = require("standard-http-error")
var app = require("express")()

app.get("/account", function(req, res, next) {
  if (req.account == null) throw new HttpError(401)
  if (req.account.budget == 0) throw new HttpError(402)
  // ...
})

app.use(function(err, req, res, next) {
  if (!(err instanceof HttpError)) return void next(err)

  res.statusCode = err.code
  res.statusMessage = err.message
  res.render("error", {title: err.message})
})

Error Codes ----------- StandardHttpError.js comes with a list of status message constants that you can use for comparison and in `switch` statements.

HttpError.NOT_FOUND // => 404

The names are generated automatically from Node.js's Http.STATUS_CODES object during run-time, so they'll always be up to date. Here's the list for reference as of Node v0.11:

Code	Name
100	CONTINUE
101	SWITCHING_PROTOCOLS
102	PROCESSING
200	OK
201	CREATED
202	ACCEPTED
203	NON_AUTHORITATIVE_INFORMATION
204	NO_CONTENT
205	RESET_CONTENT
206	PARTIAL_CONTENT
207	MULTI_STATUS
300	MULTIPLE_CHOICES
301	MOVED_PERMANENTLY
302	MOVED_TEMPORARILY
303	SEE_OTHER
304	NOT_MODIFIED
305	USE_PROXY
307	TEMPORARY_REDIRECT
308	PERMANENT_REDIRECT
400	BAD_REQUEST
401	UNAUTHORIZED
402	PAYMENT_REQUIRED
403	FORBIDDEN
404	NOT_FOUND
405	METHOD_NOT_ALLOWED
406	NOT_ACCEPTABLE
407	PROXY_AUTHENTICATION_REQUIRED
408	REQUEST_TIME_OUT
409	CONFLICT
410	GONE
411	LENGTH_REQUIRED
412	PRECONDITION_FAILED
413	REQUEST_ENTITY_TOO_LARGE
414	REQUEST_URI_TOO_LARGE
415	UNSUPPORTED_MEDIA_TYPE
416	REQUESTED_RANGE_NOT_SATISFIABLE
417	EXPECTATION_FAILED
418	IM_A_TEAPOT
422	UNPROCESSABLE_ENTITY
423	LOCKED
424	FAILED_DEPENDENCY
425	UNORDERED_COLLECTION
426	UPGRADE_REQUIRED
428	PRECONDITION_REQUIRED
429	TOO_MANY_REQUESTS
431	REQUEST_HEADER_FIELDS_TOO_LARGE
500	INTERNAL_SERVER_ERROR
501	NOT_IMPLEMENTED
502	BAD_GATEWAY
503	SERVICE_UNAVAILABLE
504	GATEWAY_TIME_OUT
505	HTTP_VERSION_NOT_SUPPORTED
506	VARIANT_ALSO_NEGOTIATES
507	INSUFFICIENT_STORAGE
509	BANDWIDTH_LIMIT_EXCEEDED
510	NOT_EXTENDED
511	NETWORK_AUTHENTICATION_REQUIRED

License

StandardHttpError.js is released under a Lesser GNU Affero General Public License, which in summary means:

• You can use this program for no cost.
• You can use this program for both personal and commercial reasons.
• You do not have to share your own program's code which uses this program.
• You have to share modifications (e.g. bug-fixes) you've made to this program.

For more convoluted language, see the LICENSE file.

About

Andri Möll typed this and the code.
Monday Calendar supported the engineering work.

If you find StandardHttpError.js needs improving, please don't hesitate to type to me now at [e-mail] or create an issue online.

Changelog

1.0.1 (Feb 23, 2015)

• Fixes subclassing example in README.