---
description: Update React state by returning a new value.
globs: "**/*.{ts,tsx}"
alwaysApply: false
---

# Immutable state

- Do not push, splice, or assign into an object that is already in state.
- Build the next array or object, then set state to that value.
- For a click handler that updates a list, copy the list first.
- If two screens show the same fact, they should read one store, not two copies that drift.