Use async function without callback.

index.js

const {promisify} = require('util');
const fs = require('fs');
const readFileAsync = promisify(fs.readFile);

const filePath = 'index.js';

async function main() {
  try {
    let text = await readFileAsync(filePath, {encoding: 'utf8'});
    console.log(text);
  } catch (error) {
    console.log(error);
  }
}

main().then();