finalhandler

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

Installation

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install finalhandler

API

const 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 or res will be terminated if a response has already started.

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).

options.contentTypeNegotiation

Enables content type negotiation based on the Accept header. When enabled, error responses will use text/plain or text/html based on the client's preferences. Defaults to false.

Warning

This will be enabled by default in the next major version.

options.defaultContentType

The fallback content type for responses when content negotiation is disabled or no preferred type can be determined. Allowed Values are text/html or text/plain. Defaults to text/html.

Warning

The default will be changed to text/plain in the next major version.

Examples

always 404

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

const server = http.createServer((req, res) => {
  const done = finalhandler(req, res)
  done()
})

server.listen(3000)

perform simple action

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

const server = http.createServer((req, res) => {
  const done = finalhandler(req, res)

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

server.listen(3000)

use with middleware-style functions

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

const serve = serveStatic('public')

const server = http.createServer((req, res) => {
  const done = finalhandler(req, res)
  serve(req, res, done)
})

server.listen(3000)

keep log of all errors

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

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

  fs.readFile('index.html', (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