node return callback as promise code example

Example 1: convert functoin with call back to promise

const readFilePromise = () => {
  return new Promise((resolve, reject) => {
    fs.readFile(filePath, options, (err, data) => {
      if (err) return reject(err)
      resolve(data)
    })
  })
}

Example 2: node js callback

function processData (callback) {
  fetchData(function (err, data) {
    if (err) {
      console.log("An error has occurred. Abort everything!");
      return callback(err);
    }
    data += 1;
    callback(null, data);
  });
}

processData(function (err, data) {
  if (err) {
      console.err(err);
  } else {
    console.log("Data: " + data);
  }
});