React: What are React 19 Server Functions?

1"use server";
2
3export async function createPost(formData: FormData) {
4  const title = formData.get("title") as string;
5  const content = formData.get("content") as string;
6
7  await db.posts.create({ data: { title, content } });
8  revalidatePath("/posts");
9}
10
11// Client Component
12import { createPost } from "./actions";
13
14function PostForm() {
15  return (
16    <form action={createPost}>
17      <input name="title" placeholder="Title" />
18      <textarea name="content" placeholder="Content" />
19      <button type="submit">Create Post</button>
20    </form>
21  );
22}

1import { useActionState } from "react";
2
3function PostForm() {
4  const [state, formAction, isPending] = useActionState(
5    async (prev, formData) => {
6      const result = await createPost(formData);
7      if (result.error) return { error: result.error };
8      redirect("/posts");
9    },
10    null
11  );
12
13  return (
14    <form action={formAction}>
15      <input name="title" />
16      {state?.error && <p className="error">{state.error}</p>}
17      <button disabled={isPending}>Create</button>
18    </form>
19  );
20}