StandardHttpError.js

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. Also works in the browser through Browserify.

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.

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})
})

HttpError.NOT_FOUND // => 404

When running on Node.js, cached status codes and their names get merged with new codes from Http.STATUS_CODES. Existing status codes will not be changed without bumping StandardHttpError.js's major version number. That ensures consistent constants in Node and in the browser.

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 208 | ALREADY_REPORTED 226 | IM_USED 300 | MULTIPLE_CHOICES 301 | MOVED_PERMANENTLY 302 | FOUND 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_TIMEOUT 409 | CONFLICT 410 | GONE 411 | LENGTH_REQUIRED 412 | PRECONDITION_FAILED 413 | PAYLOAD_TOO_LARGE 414 | URI_TOO_LONG 415 | UNSUPPORTED_MEDIA_TYPE 416 | RANGE_NOT_SATISFIABLE 417 | EXPECTATION_FAILED 418 | IM_A_TEAPOT 421 | MISDIRECTED_REQUEST 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_TIMEOUT 505 | HTTP_VERSION_NOT_SUPPORTED 506 | VARIANT_ALSO_NEGOTIATES 507 | INSUFFICIENT_STORAGE 508 | LOOP_DETECTED 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 [email protected] or create an issue online.