How to read file with async/await properly?

Since Node v11.0.0 fs promises are available natively without promisify:

const fs = require('fs').promises;
async function loadMonoCounter() {
    const data = await fs.readFile("monolitic.txt", "binary");
    return Buffer.from(data);
}

To use await/async you need methods that return promises. The core API functions don't do that without wrappers like promisify:

const fs = require('fs');
const util = require('util');

// Convert fs.readFile into Promise version of same    
const readFile = util.promisify(fs.readFile);

function getStuff() {
  return readFile('test');
}

// Can't use `await` outside of an async function so you need to chain
// with then()
getStuff().then(data => {
  console.log(data);
})

As a note, readFileSync does not take a callback, it returns the data or throws an exception. You're not getting the value you want because that function you supply is ignored and you're not capturing the actual return value.

This is TypeScript version of @Joel's answer. It is usable after Node 11.0:

import { promises as fs } from 'fs';

async function loadMonoCounter() {
    const data = await fs.readFile('monolitic.txt', 'binary');
    return Buffer.from(data);
}