React State Not Updating - Component Doesn't Re-render

1. Mutating state directly instead of creating new reference: state.obj.prop = newValue (WRONG)
2. Not creating new array/object: setState([...state, item]) works, state.push(item) doesn't
3. Setting state to same reference (React sees no change): setState(state)
4. Async state update where component unmounts before update
5. setState in useCallback without dependency causing stale closures

Always create new references: setState({...state, key: newValue}) for objects

For arrays: setState([...state, newItem]) or setState(state.filter(...))

Use immutable patterns: setState(prev => ({...prev, key: value}))

Check DevTools - if state actually updates but UI doesn't, it's an immutability issue

For complex state: consider useReducer for clearer intent