finalhandler

What is finalhandler?

The finalhandler npm package is a Node.js module designed to ensure that the final response is sent to the client. It acts as a final step in the request-response cycle, handling any remaining tasks such as sending a 404 response if no middleware has handled the request, or handling errors that may have occurred during the request processing.

What are finalhandler's main functionalities?

Error Handling

This code demonstrates how finalhandler can be used to handle errors that occur during the request processing. If an error is thrown, finalhandler will ensure that an appropriate HTTP error response is sent to the client.

const finalhandler = require('finalhandler');
const http = require('http');

http.createServer(function (req, res) {
  const done = finalhandler(req, res);
  throw new Error('Something went wrong!');
}).listen(3000);

Uncaught Exception Handling

This code sample shows how finalhandler can handle exceptions that are not caught within the context of the request. It ensures that the server remains operational and sends an error response to the client.

const finalhandler = require('finalhandler');
const http = require('http');

http.createServer(function (req, res) {
  const done = finalhandler(req, res);
  process.nextTick(function () {
    throw new Error('Async error!');
  });
  done();
}).listen(3000);

404 Not Found Response

This example illustrates how finalhandler can be used to send a 404 Not Found response when no middleware or routes have handled the request.

const finalhandler = require('finalhandler');
const http = require('http');

http.createServer(function (req, res) {
  const done = finalhandler(req, res);
  // No routes or middleware respond
  done();
}).listen(3000);

Other packages similar to finalhandler

on-finished

The 'on-finished' package is similar to finalhandler in that it is used to execute a callback when a HTTP response is finished or when an error occurs. It is a lower-level utility than finalhandler and does not handle the response itself, but rather provides a way to detect when the response has been completed.

connect

Connect is an extensible HTTP server framework for node, which uses 'middleware' to enhance Node.js features. While not a direct alternative to finalhandler, it includes similar error handling and final response capabilities within its middleware stack.

README

finalhandler

Node.js function to invoke as the final step to respond to HTTP request.

Installation

$ npm install finalhandler

API

var finalhandler = require('finalhandler')

finalhandler(req, res, [options])

Returns function to be invoked as the final step for the given req and res. This function is to be invoked as fn(err). If err is falsy, the handler will write out a 404 response to the res. If it is truthy, an error response will be written out to the res, and res.statusCode is set from err.status.

options.env

By default, the environment is determined by NODE_ENV variable, but it can be overridden by this option.

options.onerror

Provide a function to be called with the err when it exists. Can be used for writing errors to a central location without excessive function generation. Called as onerror(err, req, res).

Examples

always 404

var finalhandler = require('finalhandler')
var http = require('http')

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res)
  done()
})

server.listen(3000)

perform simple action

var finalhandler = require('finalhandler')
var fs = require('fs')
var http = require('http')

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res)

  fs.readFile('index.html', function (err, buf) {
    if (err) return done(err)
    res.setHeader('Content-Type', 'text/html')
    res.end(buf)
  })
})

server.listen(3000)

use with middleware-style functions

var finalhandler = require('finalhandler')
var http = require('http')
var serveStatic = require('serve-static')

var serve = serveStatic('public')

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res)
  serve(req, res, done)
})

server.listen(3000)

keep log of all errors

var finalhandler = require('finalhandler')
var fs = require('fs')
var http = require('http')

var server = http.createServer(function (req, res) {
  var done = finalhandler(req, res, {onerror: logerror})

  fs.readFile('index.html', function (err, buf) {
    if (err) return done(err)
    res.setHeader('Content-Type', 'text/html')
    res.end(buf)
  })
})

server.listen(3000)

function logerror(err) {
  console.error(err.stack || err.toString())
}

License

The MIT License (MIT)

Copyright (c) 2014 Douglas Christopher Wilson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.