// under NODE.js

const fs = require('fs');

const readFile = (filePath) => {
  return new Promise((resolve, reject) => {
    fs.readFile(filePath, 'utf8', (error, data) => {
      if (error) {
        reject(error);
      } else {
        resolve(data);
      }
    });
  });
}

readFile('./your-file.txt')
  .then(data => {
    console.log(`${data}`);
  }, (error) => {
    console.error(error);
  });