> For the complete documentation index, see [llms.txt](https://bryan-guner.gitbook.io/my-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bryan-guner.gitbook.io/my-docs/redux/repos/examples/real-world/node_modules/finalhandler.md).

# finalhandler

[![NPM Version](https://img.shields.io/npm/v/finalhandler.svg)](https://npmjs.org/package/finalhandler) [![NPM Downloads](https://img.shields.io/npm/dm/finalhandler.svg)](https://npmjs.org/package/finalhandler) [![Node.js Version](https://img.shields.io/node/v/finalhandler.svg)](https://nodejs.org/en/download) [![Build Status](https://img.shields.io/travis/pillarjs/finalhandler.svg)](https://travis-ci.org/pillarjs/finalhandler) [![Test Coverage](https://img.shields.io/coveralls/pillarjs/finalhandler.svg)](https://coveralls.io/r/pillarjs/finalhandler?branch=master)

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

## Installation

This is a [Node.js](https://nodejs.org/en/) module available through the [npm registry](https://www.npmjs.com/). Installation is done using the [`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):

```
$ npm install finalhandler
```

## API

```js
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`.

When an error is written, the following information is added to the response:

* The `res.statusCode` is set from `err.status` (or `err.statusCode`). If this value is outside the 4xx or 5xx range, it will be set to 500.
* The `res.statusMessage` is set according to the status code.
* The body will be the HTML of the status code message if `env` is `'production'`, otherwise will be `err.stack`.
* Any headers specified in an `err.headers` object.

The final handler will also unpipe anything from `req` when it is invoked.

#### 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

```js
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

```js
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

```js
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

```js
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

[MIT](https://github.com/bgoonz/Learning-Redux/blob/master/repos/examples/real-world/node_modules/finalhandler/LICENSE/README.md)