Note: our middleware functions are called in sequence.

app.use()

we call this method to Install a middleware function in our request processing pipeline

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next();

It is a reference to the next middleware function in the pipeline To pass control to the next middleware function in the pipeline

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//app.js
// our middleware function are called in sequence.
const logger = require("./logger");
const express = require("express");
const app = express();

//here we adding a json middleware function
app.use(express.json());

//importing Custom Middleware Function from outside
app.use(logger);

//Building Custom Middleware Function
app.use(function (req, res, next) {
  console.log("Logging...");
  next();
});

//logger.js

//Building Custom Middleware Function

function log(req, res, next) {
  console.log("Authenticating...");
  next();
}

module.exports = log;