What is dump() and duplicates() methods in Collect.js?

Collect.js - Interview Questions

dump() : The dump() method outputs the results at that moment and then continues processing:

collect([1, 2, 3, 4])
  .dump()
  .map(item => item * 2)
  .dump();

// Collection { items: [ 1, 2, 3, 4 ] }
// Collection { items: [ 2, 4, 6, 8 ] }

duplicates() : The duplicates() method retrieves and returns duplicate values from the collection:

const collection = collect(['a', 'b', 'a', 'c', 'b']);

const duplicates = collection.duplicates();

duplicates.all();

// { 2: 'a', 4: 'b' }