WHATWG file URL doc examples https://github.com/nodejs/node/pull/12670

dummy-filepath-with-hostname-posix.js

'use strict';

const fs  = require('fs');
const { URL } = require('url');
const hosts_file_url = new URL(`file://hostname/p/a/t/h/file.txt`);

fs.readFile(hosts_file_url, 'utf-8', (err,data) => {
  if (err) throw err; // error is throw
  console.log(data);
});

dummy-filepath-with-hostname-win.js

'use strict';

const fs  = require('fs');
const { URL } = require('url');
const hosts_file_url = new URL(`file://hostname/p/a/t/h/file.txt`); // path convereted to UNC

fs.readFile(hosts_file_url, 'utf-8', (err,data) => {
  if (err) throw err;  
  console.log(data); // read file's content
});

hosts-fileurl-without-hostname-posix.js

'use strict';

const fs  = require('fs');
const { URL } = require('url');
const hosts_file_url = new URL('file:///etc/hosts');

fs.readFile(hosts_file_url, 'utf-8', (err,data) => {
  if (err) throw err;
  console.log(data);
});

hosts-fileurl-without-hostname-win.js

'use strict';

const fs  = require('fs');
const { URL } = require('url');
const hosts_file_url = new URL(`file:///${process.env['SystemRoot']}/System32/drivers/etc/hosts`);

fs.readFile(hosts_file_url, 'utf-8', (err,data) => {
  if (err) throw err;
  console.log(data);
});