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Before this change, `useFormStatus` is only activated if a form is
submitted by an action function (either `<form action={actionFn}>` or
`<button formAction={actionFn}>`).
After this change, `useFormStatus` will also be activated if you call
`startTransition(actionFn)` inside a submit event handler that is
`preventDefault`-ed.
This is the last missing piece for implementing a custom `action` prop
that is progressively enhanced using `onSubmit` while maintaining the
same behavior as built-in form actions.
Here's the basic recipe for implementing a progressively-enhanced form
action. This would typically be implemented in your UI component
library, not regular application code:
```js
import {requestFormReset} from 'react-dom';
// To implement progressive enhancement, pass both a form action *and* a
// submit event handler. The action is used for submissions that happen
// before hydration, and the submit handler is used for submissions that
// happen after.
<form
action={action}
onSubmit={(event) => {
// After hydration, we upgrade the form with additional client-
// only behavior.
event.preventDefault();
// Manually dispatch the action.
startTransition(async () => {
// (Optional) Reset any uncontrolled inputs once the action is
// complete, like built-in form actions do.
requestFormReset(event.target);
// ...Do extra action-y stuff in here, like setting a custom
// optimistic state...
// Call the user-provided action
const formData = new FormData(event.target);
await action(formData);
});
}}
/>
```