Why did chrome have two requests to open a page?

  node.js, question

First, I ran this simple example.

// server.js
 'use strict';
 const http = require('http');
 http.createServer((req, res) => {
 console.log('Request received.');
 res.writeHead(200, {
 'Content-Type': 'text-plain',
 res.write('Hello World');
 console.log('Server has started.');

Then, in chrome, it openslocalhost:8888Page. Console display:

Server has started.
 Request received.
 Request received.

However, it is sometimes displayed once in firefox.Request received.Sometimes three times.
Why do browsers make multiple requests?

In general, one document and one favicon will be requested, and the rest will depend on the content.