Question from the Node.js test

const fs = require('fs');

http.createServer((req, res) => {
  let fileReader = fs.createReadStream('VeryFat.txt');
  fileReader.pipe(res);
}).listen(1337);

const fs = require('fs');
let fileContent = fs.readFileSync('VeryFat.txt', 'utf8');

http.createServer((req, res) => {
  res.end(fileContent);
}).listen(1337);

const fs = require('fs');

http.createServer((req, res) => {
  fs.readFile('VeryFat.txt', 'utf8', (err, fileContent) => {
    res.end(fileContent);
  });
}).listen(1337);

const fs = require('fs');

let fileContent = '';
fs.readFile('VeryFat.txt', 'utf8', (err, data) => {
  fileContent = data;
  server.listen(1337);
});

let server = http.createServer((req, res) => {
  res.end(fileContent);
});