Double request in Chrome with Nodejs

I'm doing a test with Nodejs to increment a global counter, according to the scripts below. Everything works, except that Chrome executes two sequential requests when I refresh it, which causes the counter to increment twice as well (see the image). In Postman and Firefox works fine and only one request occurs on refresh. I've done the tests running the app on Linux and Windows and the problem with Chrome holds. Anyone have any idea what might be happening?

server.js

const http = require('http');
const express = require('express');
const app = express();
const rotas = require("./route-test")(app);

const port = 3000;

const server = app.listen(process.env.PORT || port, function(){
    console.log('App listening port: ', port);
});

route-test.js

const myGlobalVars = require("./global-vars");

module.exports = (app) => {
    app.use('/', (req, res) => {
       res.end('Counter in: ' + myGlobalVars.counter); 
    });

    app.use(function(req, res, next){
        //console.log(req.originalUrl);
    });
}

global-vars.js

let myCounter = 0;

const _myVars = Object.create(Object.prototype, {
  dateInit: { 
    writable: false,
    configurable: false,
    value: new Date() 
  },
  counter: {
    configurable: false,
    get: function() { return myCounter++ },
    set: function(_val) {
      myCounter = _val;
    }
  }
});

module.exports = _myVars;