不可变 JS：在对象内的数组内设置对象中的属性

Question

Suppose I have an object like this:

const document = {
  items: [
    { notes: ['a', 'b'] },
    { notes: ['y', 'z'] },
  ]
}

I want to use Immutable JS to set a notes array on an item. Basically do an unshift, but immutable.

Here is what I am trying:

const immutableDocument = Immutable.fromJs(document);
immutableDocument.setIn(['items[index]', 'notes'], [newNote, ...oldNotes]);

It's not working, and I don't see anything in the documentation about accessing an array by a certain index (or predicate for that matter) within an Immutable object.

How would I accomplish this?

Update: Based on the answer on this question , I also tried immutableDocument.setIn(['items', index, 'notes'], [newNote, ...oldNotes]) , and that does not seem to work either.

Answer 1

This worked:

const newDocument = Immutable.setIn(immutableDocument, ['items', index, 'notes'], [newNote, ...oldNotes]);

Not entirely sure why the other one didn't work based on the docs , but hey, I get to move on.