`unstable_usePrompt`

The unstable_usePrompt hook allows you to prompt the user for confirmation via window.confirm prior to navigating away from the current location.

This only works for client-side navigations within your React Router application and will not block document requests. To prevent document navigations you will need to add your own `beforeunload` event handler.

Blocking a user from navigating is a bit of an anti-pattern, so please carefully consider any usage of this hook and use it sparingly. In the de-facto use case of preventing a user navigating away from a half-filled form, you might consider persisting unsaved state to `sessionStorage` and automatically re-filling it if they return instead of blocking them from navigating away.

We do not plan to remove the `unstable_` prefix from this hook because the behavior is non-deterministic across browsers when the prompt is open, so React Router cannot guarantee correct behavior in all scenarios. To avoid this non-determinism, we recommend using `useBlocker` instead which also gives you control over the confirmation UX.

function ImportantForm() {
  const [value, setValue] = React.useState("");

  // Block navigating elsewhere when data has been entered into the input
  unstable_usePrompt({
    message: "Are you sure?",
    when: ({ currentLocation, nextLocation }) =>
      value !== "" &&
      currentLocation.pathname !== nextLocation.pathname,
  });

  return (
    <Form method="post">
      <label>
        Enter some important data:
        <input
          name="data"
          value={value}
          onChange={(e) => setValue(e.target.value)}
        />
      </label>
      <button type="submit">Save</button>
    </Form>
  );
}