Consider following example:

var middleware = {    requireAuthentication: function(req, res, next) {        console.log('private route list!');        next();    },    logger: function(req, res, next) {       console.log('Original request hit : '+req.originalUrl);       next();    }}

Now you can add multiple middleware using the following code:

app.get('/', [middleware.requireAuthentication, middleware.logger], function(req, res) {    res.send('Hello!');});

So, from above piece of code, you can see that "requireAuthentication" and "logger" are two different middlewares added.

It's not saying "infinitely", but it does say that you can add multiple middleware functions (called "callbacks" in the documentation) here:

router.METHOD(path, [callback, ...] callback)

...

You can provide multiple callbacks, and all are treated equally, and behave just like middleware, except that these callbacks may invoke next('route') to bypass the remaining route callback(s). You can use this mechanism to perform pre-conditions on a route then pass control to subsequent routes when there is no reason to proceed with the route matched.

As you can see, there's not distinction between a middleware function and the function that commonly handles the request (the one which is usually the last function added to the list).

Having 10 shouldn't be a problem (if you really need to).

Express version "express": "^4.17.1" or above

From the document: Series of Middleware

var r1 = express.Router();r1.get('/', function (req, res, next) {  next();});var r2 = express.Router();r2.get('/', function (req, res, next) {  next();});app.use(r1, r2);

Let's try a real life example:

tourController.js

 exports.checkBody = (req, res, next)=>{ // middleware 1    if (!req.body.price){        return res.status(400).json({            status:'fail',            message:'Missing price!!!'        })    }    next();  } exports.createTour = (req, res) => { // middleware 2    tours.push(req.body);    fs.writeFile(      `${__dirname}/dev-data/data/tours-simple.json`,      JSON.stringify(tours),      (err) => {        res.status(201).json({          status: 'success',          data: {            tour: newTour,          },        });      }    );  };

tourRouter.js

const express = require('express');const tourController = require('./../controller/tourController')const router = express.Router();router.route('/').get(tourController.getAllTours).post(tourController.checkBody, tourController.createTour); //muliple Middleware in post route

app.js

const express = require('express');const tourRouter = require('./route/tourRouter');const app = express();app.use(express.json());app.use('/api/v1/tours', tourRouter);module.exports = app;