I haven't worked frontend in a long time but just from reading that snippet I would assume React does a `obj===obj` (identity) comparison for state update under the hood, while Svelte/Solid are doing a Proxy trap on the accessors like `parent.obj =` would result in an intercept fn being called when you hit that 'obj' access. Proxy being a little more complicated to reason about and setup in totality but a lot more powerful and flexible.