Traduci questa pagina

Usare middleware

Express is a routing and middleware web framework with minimal functionality of its own: an Express application is essentially a series of middleware function calls executed during the request-response cycle.

Middleware functions are functions that have access to:

  • The request object (req)
  • The response object (res)
  • The next middleware function in the application’s request-response cycle, commonly named next

Le funzioni Middleware possono eseguire le seguenti attività:

  • Esegue qualsiasi codice.
  • Modify the request and response objects.
  • Terminare il ciclo richiesta-risposta.
  • Pass control to the next middleware function.

If a middleware function does not end the request-response cycle, it must call next() to pass control to the next middleware function. In caso contrario, la richiesta sarà sospesa.

Un’applicazione Express può utilizzare i seguenti tipi di middleware:

È possibile caricare il middleware a livello di applicazione e router con un percorso di montaggio opzionale. Multiple middleware functions can also be loaded together, which creates a middleware sub-stack at a mount point.

Middleware a livello di applicazione

Bind application-level middleware to an instance of the app object by using the app.use() and app.METHOD() functions, where METHOD is the lowercase HTTP method of the request that the middleware function handles, such as get, post, put, or delete.

Middleware without a mount path

The following middleware function runs every time the app receives a request:

index.cjs
const express = require('express');
const app = express();


app.use((req, res, next) => {
  console.log('Time:', Date.now());
  next();
});

Middleware mounted on a path

The following middleware function runs for any type of HTTP request on the /user/:id path:

app.use('/user/:id', (req, res, next) => {
  console.log('Request Type:', req.method);
  next();
});

Gestori del percorso

Questo esempio mostra un percorso e la sua funzione di gestore (sistema middleware). La funzione gestisce le richieste GET al percorso /user/:id.

app.get('/user/:id', (req, res) => {
  res.send('USER');
});

Middleware sub-stacks

Multiple middleware functions can be loaded together at a mount point to form a middleware sub-stack. This example prints request info for any type of HTTP request to the /user/:id path:

app.use(
  '/user/:id',
  (req, res, next) => {
    console.log('Request URL:', req.originalUrl);
    next();
  },
  (req, res, next) => {
    console.log('Request Type:', req.method);
    next();
  }
);

Multiple route handlers

I gestori del percorso consentono di definire percorsi multipli per un percorso. L’esempio sottostante definisce due percorsi per le richieste GET al percorso /user/:id. Il secondo percorso non causerà alcun problema, ma non verrà mai chiamato perché il primo percorso termina il ciclo richiesta-risposta.

app.get(
  '/user/:id',
  (req, res, next) => {
    console.log('ID:', req.params.id);
    next();
  },
  (req, res) => {
    res.send('User Info');
  }
);


// handler for the /user/:id path, which prints the user ID
app.get('/user/:id', (req, res) => {
  res.send(req.params.id);
});

Skipping to the next route

Call next('route') to skip the remaining middleware functions in a router middleware stack and pass control to the next route.

Note

next('route') will work only in middleware functions that were loaded by using the app.METHOD() or router.METHOD() functions.

In the following example, if the user ID is 0, the first handler skips to the next route, which sends a special response:

app.get(
  '/user/:id',
  (req, res, next) => {
    // if the user ID is 0, skip to the next route
    if (req.params.id === '0') next('route');
    // otherwise pass the control to the next middleware function in this stack
    else next();
  },
  (req, res) => {
    // send a regular response
    res.send('regular');
  }
);


// handler for the /user/:id path, which sends a special response
app.get('/user/:id', (req, res) => {
  res.send('special');
});

Reusable middleware arrays

Middleware functions can also be grouped into arrays for better reusability. Questo esempio mostra un array con un sub-stack middleware che gestisce le richieste GET al percorso /user/:id

function logOriginalUrl(req, res, next) {
  console.log('Request URL:', req.originalUrl);
  next();
}


function logMethod(req, res, next) {
  console.log('Request Type:', req.method);
  next();
}


const logStuff = [logOriginalUrl, logMethod];
app.get('/user/:id', logStuff, (req, res) => {
  res.send('User Info');
});

Router-level middleware

Router-level middleware works the same way as application-level middleware, except it is bound to an instance of express.Router().

const router = express.Router();

Carica il middleware a livello router usando le funzioni router.use() e router.METHOD().

Il seguente esempio di codice replica il sistema middleware che viene mostrato sopra per il middleware a livello di applicazione, utilizzando il middleware a livello di router:

index.cjs
const express = require('express');
const app = express();
const router = express.Router();


// a middleware function with no mount path. This code is executed for every request to the router
router.use((req, res, next) => {
  console.log('Time:', Date.now());
  next();
});


// a middleware sub-stack shows request info for any type of HTTP request to the /user/:id path
router.use(
  '/user/:id',
  (req, res, next) => {
    console.log('Request URL:', req.originalUrl);
    next();
  },
  (req, res, next) => {
    console.log('Request Type:', req.method);
    next();
  }
);


// a middleware sub-stack that handles GET requests to the /user/:id path
router.get(
  '/user/:id',
  (req, res, next) => {
    // if the user ID is 0, skip to the next route
    if (req.params.id === '0') next('route');
    // otherwise pass control to the next middleware function in this stack
    else next();
  },
  (req, res) => {
    // render a regular page
    res.render('regular');
  }
);


// handler for the /user/:id path, which renders a special page
router.get('/user/:id', (req, res) => {
  console.log(req.params.id);
  res.render('special');
});


// mount the router on the app
app.use('/', router);

Skipping out of a router

Use next('router') to skip the rest of the router’s middleware functions and pass control back out of the router instance.

In the following example, the router only responds when the request includes an x-auth header. Otherwise, next('router') exits the router and the app responds with a 401 status:

index.cjs
const express = require('express');
const app = express();
const router = express.Router();


// predicate the router with a check and bail out when needed
router.use((req, res, next) => {
  if (!req.headers['x-auth']) return next('router');
  next();
});


router.get('/user/:id', (req, res) => {
  res.send('hello, user!');
});


// use the router and 401 anything falling through
app.use('/admin', router, (req, res) => {
  res.sendStatus(401);
});

middleware gestione errori

Definire le funzioni middleware per la gestione degli errori allo stesso modo di altre funzioni middleware, tranne con quattro argomenti invece di tre, specificatamente con la firma (err, req, res, next):

app.use((err, req, res, next) => {
  console.error(err.stack);
  res.status(500).send('Something broke!');
});

La gestione degli errori del middleware richiede sempre four argomenti. È necessario fornire quattro argomenti per identificarlo come una funzione middleware di gestione degli errori. Anche se non è necessario utilizzare l’oggetto next , è necessario specificarlo per mantenere la firma. Otherwise, the next object will be interpreted as regular middleware and will fail to handle errors.

Middleware incorporato

Express ha le seguenti funzioni middleware integrate:

middleware di terze parti

Usa middleware di terze parti per aggiungere funzionalità alle app Express.

Installare il modulo Node.js per le funzionalità richieste, quindi caricarlo nell’app a livello di applicazione o a livello di router.

L’esempio seguente illustra l’installazione e il caricamento della funzione middleware di analisi dei cookie cookie-parser.

Terminal window
npm install cookie-parser
index.cjs
const express = require('express');
const app = express();
const cookieParser = require('cookie-parser');


// load the cookie-parsing middleware
app.use(cookieParser());