http-errors

Install the http-errors module using the npm registry.

$ npm install http-errors

You can use http-errors within Express middleware to trigger error handling by passing a created error to the next() function.

var createError = require('http-errors')
var express = require('express')
var app = express()

app.use(function (req, res, next) {
  if (!req.user) return next(createError(401, 'Please login to view this page.'))
  next()
})

Extends an existing error object with createError.HttpError properties. This does not change the inheritance of the original error object; it simply attaches the HTTP properties and returns the modified error.

• status: The status code as a number.
• error: The existing error object to extend.
• properties: An object containing custom properties to attach.

fs.readFile('foo.txt', function (err, buf) {
  if (err) {
    if (err.code === 'ENOENT') {
      var httpError = createError(404, err, { expose: false })
    } else {
      var httpError = createError(500, err)
    }
  }
})

Creates a new error object that inherits from createError.HttpError.

• status: The status code as a number.
• message: The error message. If omitted, it defaults to the standard Node.js text for that status code.
• properties: An object containing custom properties to attach to the error object.

var err = createError(404, 'This video does not exist!')

You can create specific HTTP errors using named constructors available on the createError object. These constructors inherit from createError.HttpError.

Example usage:

var err = new createError.NotFound()

Every error object created by http-errors contains the following properties:

• expose: A boolean indicating if the message should be sent to the client. Defaults to false when status >= 500.
• headers: An object of header names to values to be sent to the client (e.g., { 'www-authenticate': '...' }). Keys must be lower-cased. Defaults to undefined.
• message: The error message string.
• status: The HTTP status code.
• statusCode: The HTTP status code (mirrors status for compatibility). Defaults to 500.

Use isHttpError(val) to determine if a given value is a valid HTTP error object produced by this library.

A value is considered an HTTP error if:

1. It is an instance of HttpError.
2. OR it is an Error object that has an expose property (boolean), a statusCode property (number), and where status === statusCode.

The createError module exports specific constructors for every HTTP status code and their corresponding message identifiers. This allows you to use new to create specific error types.

For example, if the status 404 has the message Not Found, you can use createError[404] or createError.NotFound to instantiate the error.

• 4xx Errors: These are treated as client errors and have expose: true.
• 5xx Errors: These are treated as server errors and have expose: false.

The HttpError property on the exported module is an abstract base class that inherits from Error. It is used for type checking via instanceof.

Note: You cannot instantiate HttpError directly; attempting to do so will throw a TypeError.