const fs = require('fs').promises;
const read_file = (fname) =>
fs.open(fname, 'r')
.then(fh => fh.stat().then(stat => [fh, stat]))
.then(res =>
res[0].read(Buffer.alloc(res[1].size), 0, res[1].size, null))
.then(result =>
console.log(`Read ${result.bytesRead} bytes: ${result.buffer.toString()}`))
.catch(err => console.error(err))
read_file('test.txt');