[Suggestion]: Provide examples for useActionState with onSubmit handlers

[anthonyalayo]

Summary

Add examples to the useActionState documentation showcasing how it can work inside onSubmit handlers of forms.

Page

https://react.dev/reference/react/useActionState

Details

The docs show how to use useActionState with the action property of a form. However, the docs don't show how to use useActionState when you need to use it from onSubmit instead. This has been something that I have been fighting.

Let's say you are developing a multi-step / wizard form across multiple components. Not all of the form is rendered at the same time, so uncontrolled components won't work here. You need to use controlled components for your input fields in order to keep all the form state as you go through steps.

When it comes to submission, using action={formAction} won't work anymore, because that will only submit with the input fields currently rendered. It is not at all clear what the expectations are for doing this in the onSubmit handler instead.

When I attempt to do something like this:

        <form
          onSubmit={form.onSubmit(async (values, event) => {
            const formData = new FormData();

            for (const [key, value] of Object.entries(values)) {
              formData.append(key, value);
            }

            startTransition(async () => {
              await formAction(formData);
            });
          })}
        >

I get interesting messages like TS80007: await has no effect on the type of this expression. on the line calling my form action, and I can't await the result and/or handle it.