HTTP Error classes in Node.js

http-errors.js

'use strict';
const statusCodes = require('http').STATUS_CODES;

function createError(code, name) {
  return function(message) {
    Error.captureStackTrace(this, this.constructor);
    this.name = name;
    this.message = message;
    this.statusCode = code;
  }
}

Object.keys(statusCodes)
  .filter(code => code >= 400)
  .forEach(code => { 
    let name = statusCodes[code]
      .replace(/\W/g, '')
      .concat('Error')
    exports[name] = createError(Number(code), name);
    require('util').inherits(exports[name], Error);
  })

node-http-errors.md

4xx/5xx errors with their statusCode in it.

Usage

var BadRequestError = require('./http-errors').BadRequestError;

function doSomethingBad() {
  throw new BadRequestError('It went bad!');
}

try {
  doSomethingBad();
} catch (err) {
  assert.strictEqual(err.statusCode, 400);
}

Features

• 4xx/5xx status as errors classes - Status text is the class name, e.g. UnauthorizedError, NotFoundError
• Status code property - Error handlers can use the status code to send responses.
• Correct stack trace - no extra stack frames, no double capturing of the stack trace

Anti-patterns

These are some things that I've seen in other proposed solutions that you should avoid.

• Error.call(this) - creates another error object (wasting a bunch of time) and doesn't touch this at all
• Error.captureStackTrace(this, arguments.callee); - works, but arguments.callee is deprecated, so don't use it
• this.stack = (new Error).stack - this... I don't even...

test-error.js

// Mini test suite for our 4xx/5xx error

var assert = require('assert');
var BadRequestError = require('./http-errors').BadRequestError

function doSomethingBad() {
  throw new BadRequestError('It went bad!');
}

try {
  doSomethingBad();
} catch (err) {
  // The name property should be set to the error's name
  assert(err.name = 'BadRequestError');
  // The error should be an instance of its class
  assert(err instanceof BadRequestError);
  // The error should be an instance of builtin Error
  assert(err instanceof Error);
  // The error should be recognized by Node.js' util#isError
  assert(require('util').isError(err));
  // The error should have recorded a stack
  assert(err.stack);
  // toString should return the default error message formatting
  assert.strictEqual(err.toString(), 'BadRequestError: It went bad!');
  // The stack should start with the default error message formatting
  assert.strictEqual(err.stack.split('\n')[0], 'BadRequestError: It went bad!');
  // The first stack frame should be the function where the error was thrown.
  assert.strictEqual(err.stack.split('\n')[1].indexOf('doSomethingBad'), 7);
  // The extra property should have been set
  assert.strictEqual(err.statusCode, 400);
}