How to remove duplicate objects by a field

Short answer

Keep the first object with each value of the field, remembering seen values in a Set:

const users = [
  { id: 1, name: 'Anna' },
  { id: 2, name: 'Oleg' },
  { id: 1, name: 'Anna (copy)' },
];
const seen = new Set();
const unique = users.filter((user) => {
  if (seen.has(user.id)) return false;
  seen.add(user.id);
  return true;
});
 
console.log(unique.map((user) => user.name).join(', '));

Output:

Anna, Oleg

Keep the last one

A Map with the field as the key overwrites earlier objects, so the last one wins:

const users = [
  { id: 1, name: 'Anna' },
  { id: 2, name: 'Oleg' },
  { id: 1, name: 'Anna (updated)' },
];
const unique = [...new Map(users.map((user) => [user.id, user])).values()];
 
console.log(unique.map((user) => user.name).join(', '));

Output:

Anna (updated), Oleg

Common mistake

new Set() does not help with objects directly: it compares them by reference, and different objects are always different:

const users = [{ id: 1 }, { id: 1 }];
 
console.log(new Set(users).size);

Output:

Thanks for reading!

Short answer

Keep the last one

Common mistake

Functions used in this recipe

Thanks for reading!