Next.js App Router: Is it worth implementing in your next project?

What is the App Router?

The app router is a new routing system introduced in Next.js version 13. As mentioned, the file structure dictates which version you’ll use. In the app router, the core of the project is placed in the src/app directory. Next.js has added many helpful features, which give you more control over the file structure. While this requires a bit more understanding from the developer and raises the learning curve, it becomes an enjoyable and flexible system to work with once you dive into this approach.

Key features of an app router

1. Client vs. Server Components: App routers allow you to separate components based on where they operate — on the server or in the browser. This distinction enables better performance, with server components handling more intensive tasks, while client components focus on user interactivity.

source: Next.js documentation

2. Simplified Layout Management: Using layout.js makes creating and managing layouts straightforward. Nested layouts make it easy to handle complex page structures with organized hierarchy and reusability.

source: Next.js documentation

3. Server Actions: App routers support executing server-side functions in response to user actions on the client side, which can be useful for tasks like form submissions and data mutations.

4. SEO Optimization: App routers provide built-in tools for managing SEO, so metadata can be handled directly within the app router. This makes the SEO setup simpler and more integrated.

source: Next.js documentation

5. Built-in Sitemaps mechanism: Next.js introduced a dedicated sitemap.(js|ts) file convention for programmatically generating sitemaps. By creating this file, you can easily set up a sitemap without additional configuration. This built-in mechanism makes generating a sitemap simpler than ever, helping search engines more effectively index your application.

source: Next.js documentation

6. Route Groups: With route groups, you can organize your application’s routes into specific groups, making it easier to manage complex structures. This keeps your project organized and helps you control which sections of the app share certain components or layouts.

source: Next.js documentation

7. Simple API Creation: Creating an API is straightforward with the Next.js app router. By adding files in specific directories, you can quickly set up API endpoints that allow data to be fetched, updated, or sent to other parts of the app.

source: Next.js documentation

8. Parallel and Sequential Data Fetching: The Next.js app router supports both parallel and sequential data fetching. Parallel fetching allows multiple data requests to happen simultaneously, speeding up the loading process. Sequential fetching, on the other hand, lets you control the order in which data is loaded, which can be useful for handling dependencies between data requests.

source: Next.js documentation

9. Soft navigation - traditional browsers perform a "hard navigation" when moving between pages, meaning the entire page reloads. With the Next.js App Router, you get "soft navigation," which only reloads the parts of the page that actually change. This partial re-rendering allows smoother transitions and preserves user data or interactions as they navigate.

10. Route-Based Caching: With the App Router, Next.js introduces more granular control over caching at the route level, allowing developers to cache specific routes and components more effectively. This can help in reducing redundant data fetching.

11. Static and Dynamic Caching Modes: The App Router now supports both static and dynamic caching. Static routes are cached automatically, while dynamic routes offer more flexible control, enabling options like revalidation at set intervals (ISR – Incremental Static Regeneration).

source: Next.js documentation

Advantages of using an app router

Using an app router brings a lot of benefits that make things easier for both users and developers. A big advantage is how app routers improve performance. By dividing parts of the app between what runs on the server and what runs in the browser, the app can load faster and respond more quickly. The server handles the heavy lifting, while the browser focuses on interactive elements for users. App routers also let developers create reusable layouts and components, so if parts of the app’s design repeat, they don’t need to be rebuilt from scratch. This keeps things organized and helps avoid duplicate work.

App routers also make it easier to improve SEO, so developers can set up the metadata search engines need to find the app without extra effort.

Overall, the structured setup of an app router makes the codebase easier to manage and grow, which means that as the app gets more complex, the development process stays smooth and streamlined.

Potential disadvantages

1. Increased Learning Curve: The app router requires familiarity with Next.js-specific conventions, which may be challenging for developers new to the framework or to React.

2. Potential for Performance Overheads: Although the app router optimizes many aspects of an application, its more complex structure can introduce slight performance impacts, particularly if not configured carefully.

3. Migration Complexity from Page Router - Moving an existing project from the older page router to the new app router can be tricky. While you can technically use both routers in the same project, it's not recommended. Mixing them might create issues with navigation, making the experience less smooth for users as they switch between routes. This can result in “hard navigations” and a disjointed codebase, which can make it more difficult to maintain and scale your project over time.

4. Payload Size Concerns: Another thing to think about is how much data is being sent to the client. With the older page router, only the necessary data is sent, keeping the payload small. However, the app router’s model sends the entire DOM as JSON along with the HTML. This can make the payload significantly larger. While sending more data can help improve loading times on the client side, it can also lead to higher bandwidth costs due to the increased size of the data being transferred.

5. Performance Trade-offs: While the older pages router can achieve a lower First Contentful Paint (FCP) by serving HTML faster, the app router's use of server components may lead to a better Time to Interactive (TTI). Server components allow React to skip hydration for static elements, meaning less JavaScript needs to be parsed and executed. This is especially beneficial for static websites or pages with many elements, as it can significantly improve performance by avoiding unnecessary hydration.

When to use an app router

The app router in Next.js is a great choice if you want a fast, organized, and scalable web application. It’s especially useful for projects that need both server-side and client-side components, allowing you to balance heavy tasks on the server and keep the browser focused on interactive elements. While learning the app router might take a little extra effort, the built-in tools for SEO, routing, and data fetching make it an excellent option for building a powerful app that’s easy to grow and maintain.

If you already have a project using the older page router, migrating isn’t straightforward- these two routers use different setups, and the change can be tricky. However, the Next.js team officially recommends switching to the app router and there’s no knowing when the page router may be deprecated. Migrating now can make your project more future-proof.

Summary

The app router in Next.js brings several advantages, including improved performance, and organized layouts, making it a strong choice for complex, scalable applications. For SEO, it offers integrated tools and automatic sitemap generation, making optimization more straightforward.

However, using the app router comes with some challenges. It has a steeper learning curve and requires specific Next.js knowledge, especially around file structure. Migrating from a page router can be complicated due to the differences and troubles with maintaining a disjointed codebase, though Next.js officially recommends this switch.

Additionally, while the app router can improve interaction times, it may increase initial data payloads, potentially affecting load times if not managed carefully.

Next.js is aware of some of its current performance limitations and is actively working on improving them in the latest versions. The team has set clear goals to improve three key areas: speed during local development, faster production builds, and smoother performance on serverless setups.

The newly released Next.js 15 also brings promising improvements. Since it’s very new, we’re holding off on full implementation for now, but we’re hopeful that it will address some of the performance gaps found in older versions.

Overall, when deciding whether to use the app router, consider your project’s specific needs regarding performance, layout organization, and SEO. The app router offers strong advantages in these areas, making it an excellent choice for scalable, complex applications.

If you’re eager to explore more about Next.js and the app router, check out the documentation or try experimenting with its features in your project!