State Management · Senior · Question 55 of 75

What is wrong with this cache update?

queryClient.setQueryData(["todos"], (old) => {
  old.push(newTodo);
  return old;
});

✓Correct answer: It mutates cached data; return a new array, otherwise observers may not update and structural sharing breaks
2setQueryData only accepts objects
3It must be awaited

Explanation

Write (old) => old ? [...old, newTodo] : [newTodo]. Cached data is treated as immutable, just like React state.

Further reading

TanStack Query: Updates from Mutation Responses ↗

Test yourself

Take the State Management · Senior quiz: questions and options are shuffled, and you get a review of your mistakes at the end.