CODEWITHSUNDEEP
node.jsexpress
Naeem Shaikh
Naeem Shaikh

Reputation: 15725

Difference Between app.use() and router.use() in Express

I was just reading the documentation on express and found these two terms, app.use(); and router.use();

I know app.use(); is used in node for Mounting a middleware at a path, and we often use it in most of the node apps. but what is router.use(); are they both same? if not, whats the difference ?

I read about router here. I also found similar questions on SO What is the difference between "express.Router" and routing using "app.get"? and Difference between app.all('*') and app.use('/'), but they do not really answer my question. Thanks.

Upvotes: 117

Views: 108132

Answers (5)

ryanwaite28
ryanwaite28

Reputation: 2050

When looking at the express js docs for Routing (https://expressjs.com/en/guide/routing.html#express-router):

Use the express.Router class to create modular, mountable route handlers. A Router instance is a complete middleware and routing system; for this reason, it is often referred to as a “mini-app”.

A Router created with express.Router() is no different than an app created with express() in terms of functionality; it's like a logical grouping of routes/handlers/services/databases/etc. The biggest difference is the scope that it affects. A router just affects its own scope while the app is like the master/global scope for your web/app server. You could have many routers or "apps" running on one main app/web server instance. This is why you could listen to requests on an app instance via app.listen(80) but not on a router.

Upvotes: 3

nCardot
nCardot

Reputation: 6595

app.use(middleware): application-level middleware.

router.use(middleware): router-level middleware.

("middleware" refers to methods/functions/operations that are called between processing the request and sending the response.)

See https://expressjs.com/en/guide/using-middleware.html for a comparison of different types of middleware used in an Express app.

Upvotes: 1

Sudhanshu Gaur
Sudhanshu Gaur

Reputation: 7684

router.get is only for defining subpaths. Consider this example:

var router = express.Router();

app.use('/first', router); // Mount the router as middleware at path /first

router.get('/sud', smaller);

router.get('/user', bigger);
  • If you open /first/sud, then the smaller function will get called.
  • If you open /first/user, then the bigger function will get called.

In short, app.use('/first', router) mounts the middleware at path /first, then router.get sets the subpath accordingly.

But if we instead use the following:

app.use('/first', fun);

app.get('/sud', bigger);

app.get('/user', smaller);
  • If you open /first in your browser, fun will get called,
  • For /sud, bigger will get called
  • For /user, smaller will get called

But remember for /first/sud, no function will get called.

This link may also help: http://expressjs.com/api.html#router

Upvotes: 167

Shubham Verma
Shubham Verma

Reputation: 9971

app.use() used to Mounts the middleware function or functions at the specified path,the middleware function is executed when the base of the requested path matches path.

router.use() is used to middleware function or functions, The defaults mount path to “/”.

But in app.use() you will have to give a specified path like that:

 var adsRouter = require('./adsRouter.js');
    app.use('/ads', adsRouter);

or 

app.use('/ads', function(req, res, next) {

  // write your callback code here.

    });

But while using router.use() you can give only middleware, like this: 

router.use(function(req, res, next) {
  console.log('%s %s %s', req.method, req.url, req.path);
  next();
});

or 

router.use('/test', function(req, res, next) {
  // write your callback code here.
  next();
});

or

//in router.js

router.use('/admin', authUtil.verifySessionId, authUtil.verifyLisencee);
router.post('/admin', controllerIndex.ads.adListingAdmin);

In the above code when the end point is '/admin' then first it will call the authUtil.verifySessionId and authUtil.verifyLisencee then it will execute next line with 'admin' end point and according to controllerIndex.ads.adListingAdmin method.

Upvotes: 3

Laura
Laura

Reputation: 3383

router.use(); mounts middleware for the routes served by the specific router, app.use(); mounts middleware for all routes of the app (or those matching the routes specified if you use app.use('/ANYROUTESHERE', yourMiddleware());).

Example use case could be an app with one router with standard routes and one router that handles api routes, which need a valid user.

You would then mount the authentication middleware for the api router only with router.use(yourAuthMiddleware());.

If you would have an app though that requires a valid user for all routes, mount the middleware for the app with app.use(yourAuthMiddleware());

Upvotes: 102

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