Troubleshooting

Use this page when the store behaves differently than expected.

My subscriber did not run after I changed an object

You probably mutated the object in place and returned the same reference.

store.setState((prev) => {
  prev.count += 1; // mutation / in place change
  return prev;
});

Because the reference is the same, Object.is(prev, resolvedState) is true and the store does not notify. Return a new object instead.

store.setState((prev) => ({ ...prev, count: prev.count + 1 }));

My fields disappeared

setState() replaces state. It does not merge and it never performs a deep merge.

store.setState({ name: "Ada" });

If the old state also had theme, that field is gone. Preserve fields explicitly.

store.setState((prev) => ({ ...prev, name: "Ada" }));

My updater saw an unexpected value

The updater receives the state at the final application step. Middleware can transform the update before it gets there. If middleware resolves an updater early, later middleware receives a value instead of the original updater. Review middleware order and whether each middleware forwards with next().

My listener keeps running after the owner is gone

You forgot to call unsubscribe.

const unsubscribe = store.subscribe(() => render(store.getState()));

// later
unsubscribe();

Tie unsubscribe to component unmount, widget destroy, route disposal, or module shutdown.

Middleware runs in the wrong order

pushMiddleware() appends and unshiftMiddleware() prepends. The first middleware in the array receives updates first because the chain is built with reduceRight.

If order matters, write a small test or log around next() calls:

store.pushMiddleware((state, next) => {
  console.log("before A");
  next(state);
  console.log("after A");
});

getInitialState() did not reset my store

getInitialState() only reads the constructor value. Reset by passing a value to setState().

store.setState(store.getInitialState());

For object state, create a fresh object if subscribers must run even when the store currently points at the initial reference.