Question

What does the app use do in Express

Answer 1

app.use() is mounted to the specific path. So whenever this route is hit it executes the function which is inside it gets executed.

var express = require('express');
var app = express();

app.use('/application', function(req, res, next){
   console.log("Request is recieved at " + Date.now());
   next();
});

app.get('/application', function(req, res){
   res.send('express');
});
app.listen(3000);