util.promisify.js

const util = require('util');

setTimeout(async () => {

  db.getData = util.promisify(db.getData);
  db.processData = util.promisify(db.processData);
  db.saveData = util.promisify(db.saveData);
  
  try {
    const data = await db.getData();
    data.a = 'test';
    data.b = 1111;
    await db.processData(data);
    await db.saveData();
    console.log('finished');
  } catch (err) {
    console.log(err);
  }

}, 0);


// MOCK DB ---------------------------------------------

const db = {
  getData: function(callback) {
    this.hello = 'world';
    const err = null;
    callback(err, {...this});
  },
  processData: function(data, callback) {
    Object.assign(this, data);
    this.processed = true;
    const err = null;
    callback(err, {...this});
  },
  saveData: function(callback) {
    const err = null;
    this.saved = true;
    callback(err, {...this});
  },
};


// OUTDATED LIBRARY -----------------------------

db.getData((err, data)=>{
  if (err) {
    console.log(err);
    return;
  }
  data.a = 'test';
  data.b = 1111;
  db.processData(data, (err, data)=>{
    if (err) {
      console.log(err);
      return;
    }
    db.saveData((err, data)=>{
      if (err) {
        console.log(err);
        return;
      }
      console.log('finished');
    });
  });
});