Review your Express.js application performance by yourself

AppJsWithTimeMeasurement.js

// Section 1
var express = require('express');
const bodyParser = require('body-parser');
const { EventEmitter } = require('events');
const morgan = require('morgan');
const app = express();
const profilingEventEmitter = new EventEmitter();

// Section 2
profilingEventEmitter.on('middleware', ({ req, name, elapsedMS }) => {
    console.log(req.method, req.url, ':', name, `${elapsedMS}ms`);
});

// Section 3
var profiler = function(fn) {
    if (fn.length === 2) {
        return function (req, res) {
            const start = Date.now();
            res.once('finish', () => profilingEventEmitter.emit('middleware', {
                req,
                name: fn.name,
                elapsedMS: Date.now() - start
            }));
            return fn.apply(this, arguments);
        };
    } else if (fn.length === 3) {
        return function (req, res, next) {
            const start = Date.now();
            fn.call(this, req, res, function () {
                profilingEventEmitter.emit('middleware', {
                    req,
                    name: fn.name,
                    elapsedMS: Date.now() - start
                });
                next.apply(this, arguments);
            });
        };
    } else {
        throw new Error('Function must take 2 or 3 arguments');
    }
}

// Section 4
app.use(profiler(morgan('dev')));
app.use(profiler(bodyParser.json()));
app.use(profiler(express.static('public')));

// Section 5
app.get('/check', profiler(function userRequestHandling(req, res) {
    setTimeout(() => res.send('Done'), 2);
}));

app.listen(3000);