[sethaurus]

These days that's pretty well-supported in the base language:

    const updated = { ...existing, someKey: someNewValue };

You mention nesting. That starts to look messier:

    const updated = { ...existing, someKey: { ...existing.someKey, ...someNewValue } };

There's a whole cottage industry of little libraries to make this ergonomic/fast in the general case (copying immutable objects with nested changes). `immer` is a popular choice. But the reality is that it gets complicated to do this generically; in my view it's usually better to just use the base language where possible, even if it means sprouting some util functions for the various kinds of updates you end up doing.