Callback

function callbackFn(filename, callback) {
  const isError = false;

  // complex code logic
  if (isError) {
    callback(Error("Error occured from callbackFn"), null);
  } else {
    callback(null, filename);
  }
}

Function calls :

callbackFn(FILE_NAME, (error, data) => {
  if (error) {
    console.log("Error (callbackFn) : ", error);
  } else {
    console.log("Data (callbackFn)", data);
  }
});