feat: support form submission via FormData

[josiahwiebe]

This is a proposed improvement to simplify form input handling with minimal abstraction.

I'm creating this as a draft because I don't think it's necessarily dogmatic but I see it as an improvement.

After attending Leah's Inertia.js talk at React Miami, I found myself thinking the form input handling was a bit too verbose for some use cases. Currently, forms require individual onChange events for every input (updating the component state), which feels like it can be unnecessarily complex for some use-cases.

This PR adds the ability to pass the form element (target) as an option to the form.post method, which will then use native FormData to handle the payload.

For example:

function submit(e: React.FormEvent<HTMLFormElement>) {
  e.preventDefault();
  form.post('/user', {
    target: e.currentTarget,
  })
}

While this pattern might not be used everywhere, I believe it's valuable to offer a more native, standards-focused API for use-cases that require minimal abstraction.

[chasegiunta]

I wish this could be taken one step further. Why a submit handler to begin with?

What if there was a Form component?

<Form action="/user">
  <input type="text" name="fullName">
  <input type="text" name="fields[nestedField]">
  <input type="text" name="fields[nestedArrayField][]" value="new item">
  
  <button type="submit">Submit</button>
</Form>

[josiahwiebe]

I think a Form component is probably a better approach overall.

• Keep the submit handler for more complex scenarios
• Create a simpler Form component that handles FormData by default