What is use server, why and when to use it in Next.js?

The "use server" directive in Next.js is used to indicate that a function should be executed on the server side. It allows you to write server-side logic that can be called from the client side, such as handling form submissions or processing data.

You should use "use server" when you need to perform operations that require server-side capabilities, such as:

• Accessing databases or file systems
• Performing secure operations that should not be exposed to the client
• Handling form submissions and processing data on the server

Example usage:

// app/form-example/page.js
"use server";

export async function handleSubmit(formData) {
  const name = formData.get("name");
  console.log("Form submitted with name:", name);
  return { success: true };
}

export default function FormExample() {
  return (
    <form action={handleSubmit}>
      <input type="text" name="name" />
      <button type="submit">Submit</button>
    </form>
  );
}

In this example, the handleSubmit function is marked with "use server", indicating that it will run on the server when the form is submitted.