Understanding Next.js and the Need for use client and use server Directives

Next.js has rapidly become a go-to framework for building React applications, offering powerful features like server-side rendering (SSR), static site generation (SSG), and incremental static regeneration (ISR). With Next.js 13, the framework introduced the App Router and Server Components, which are aimed at further enhancing performance and developer experience. One of the key features of this release is the introduction of the use client and use server directives. In this article, we'll explore what these directives are, why they are important, and how to use them in your Next.js applications.

What are Server Components?

Before diving into use client and use server, it's essential to understand the concept of Server Components. Next.js is built on React Server Components, a feature that allows components to be rendered on the server and sent as HTML to the client. Unlike traditional SSR, Server Components enable you to split your React components into two categories:

1. Server Components: Rendered entirely on the server, without sending JavaScript to the client.
2. Client Components: Rendered on the client, just like in traditional React apps.

Server Components reduce the amount of JavaScript sent to the browser, improving load times and making your application more efficient.

What is use client?

By default, Next.js assumes that most of your components are Server Components to optimize performance. However, there are times when certain components need to run on the client, such as those involving interactivity (e.g., event handlers, state management with useState, or useEffect).

To explicitly mark a component as a Client Component, you need to add the "use client" directive at the top of the file. This tells Next.js to bundle this component's code as client-side JavaScript and run it in the browser.

Example of use client

In this example, the useState hook is used to manage component state, so we need to mark it as a client component. The "use client" directive at the top ensures that this component runs in the client environment where JavaScript can handle interactions.

What is use server?

In contrast to use client, the "use server" directive explicitly marks a function or component as a Server Component. This is useful when you want certain logic to be executed only on the server without exposing it to the client.

By default, most components in Next.js are Server Components unless you specify otherwise with use client. However, with helper functions or server-specific operations like database queries, you may need to ensure that certain code runs on the server. In these cases, you can use the use server directive.

Example of use server

Here, getData is an async function that fetches data from a database. Since databases should only be queried from the server to avoid exposing sensitive data, we use "use server" to make sure this function never runs on the client.

When to Use use client and use server

Now that we understand the basics, let's discuss some practical scenarios where these directives are necessary.

When to Use use client

1. Stateful Components: Components that rely on useState, useEffect, or any other React hook for managing state and side effects.
2. Event Listeners: Components that handle user interactions like clicks, form submissions, or any other client-side events.
3. Client-Side Libraries: Components that use browser-specific libraries like localStorage, window, or document.

When to Use use server

1. Database Queries: Functions or components that interact with a database or any other server-side service.
2. Sensitive Operations: Any operations that should be protected from being exposed to the client, such as authentication or payment processing.
3. Static Data Fetching: When you want to fetch data at build time or request time, but without sending the logic to the client.

Performance Benefits

By defaulting to Server Components, Next.js 13 allows you to ship less JavaScript to the client. Only components with interactivity need to be client-side, and those components can be isolated with use client. Server Components, on the other hand, render on the server and send pure HTML to the browser, which significantly improves page load performance.

Conclusion

Next.js's introduction of the use client and use server directives gives developers fine-grained control over where their components and functions are executed. By defaulting to Server Components, Next.js optimizes for performance, allowing you to send less JavaScript to the client while maintaining interactivity through Client Components when needed.

As you build with Next.js, keep in mind:

• Use "use client" for interactive, stateful components.
• Use "use server" for server-side logic and sensitive operations.

Mastering these directives will allow you to build efficient, scalable applications with the best of both server-side and client-side rendering.

Happy coding!