Using reduce function, I would like to get directors and their titles in a object. I accidentally initialized it as an empty array instead of an object. But I figured out that, calling Object.entries on this empty array was returning something.

And I would like to understand why this returns something. Is this about references ?

Code :

const films  = [
  { director: "Hayao Miyazaki", title: "title1" },
  { director: "Hayao Miyazaki", title: "title2" },
  { director: "Gerard", title: "title1" },
  { director: "Gerard", title: "title1" },
  { director: "Anne", title: "title1" },
];

// we want an object of directors and their titles, using reduce
const directorsFilms = films.reduce((a, { director, title }) => {
  if (!a[director]) a[director] = [];
  a[director].push(title);
  return a;
}, []); // my mistake, should have been an empty object "{}"

// prints something in PythonTutor but not in Codepen.
// referenced to an empty array
console.log(directorsFilms);

// but when you call Object.entries on this empty array, there are results
// I call Object.fromEntries to get the object I was supposed to have calling reduce, not important
const tmp = Object.fromEntries(Object.entries(directorsFilms));
console.log(tmp);

I don't understand how this is possible... I would appreciate some insight. Thanks in advance! :)