const fs = require('fs');

const read_file = (fname, cb) => {
  fs.stat(fname, (err, stats) => {
    fs.open(fname, 'r', (err, fd) => {
      let inbuf = Buffer.alloc(stats.size);
      fs.read(fd, inbuf, 0, stats.size, null, (err, bytesRead, buffer) => {
        cb(buffer);
      });
    });
  });
}

read_file('test.txt', (result) => {
  console.log(`Result is ${result.toString()}`);
});