How to get list of duplicate objects in an array of objects with JavaScript?

To get list of duplicate objects in an array of objects with JavaScript, we use some array methods.

For instance, we write

const srr = [
  { id: 10, name: "someName1" },
  { id: 10, name: "someName2" },
  { id: 11, name: "someName3" },
  { id: 12, name: "someName4" },
];

const unique = arr
  .map((e) => e.id)
  .map((e, i, final) => final.indexOf(e) === i && i)
  .filter((obj) => arr[obj])
  .map((e) => arr[e]);

to call arr.map with a callback to return an array of id property values.

Then we call map with a callback to get the index of the id value in.

And then we call filter to get the first instance of the object with the given id in arr with filter.