Next.js vs. React: A Comparative Guide for Developers

React focuses solely on the view layer, making integrating with other libraries and frameworks easy.

Next.js builds on top of React, allowing developers to use React components while handling many complexities of web development.

While both aim to improve the process of building UIs, React is a library that handles views, whereas Next.js is a framework that handles full applications. This article will investigate how they compare across factors like rendering, tooling, and more.

Web application agencies often leverage React and Next.js to streamline their development process and enhance the user experience of their applications.

Defining React

React is an open-source JavaScript library for building user interfaces. It was created by Facebook and released in 2013.

Some key features of React include:

• Component-Based: React apps are built using components that are customizable and reusable pieces of code. Components manage their own state and rendering logic. Complex UIs can be created by composing components together.
• Virtual DOM: React keeps a virtual representation of the actual DOM in memory. When the state changes, React calculates the optimal way to update the UI by comparing the virtual DOM against the previous virtual DOM state. This efficient process allows updating only necessary parts of the actual DOM.
• Uni-directional Data Flow: Data in React apps flow in one direction downwards from parent to child components. The state is only updated through setState() and data bindings. This makes the logic and data flow easy to reason about.

Defining Next.js

Next.js is a popular React framework for building server-rendered React applications. It provides a solution for static and server-side rendering right out of the box.

Some key features of Next.js:

• Hybrid Static & Server Rendering - Next.js allows you to statically generate pages at build time for fast initial page loads. It can then hydrate those pages into full React apps on the client side. Next.js handles all the transitions between static and hydrated states for you.
• Automatic page pre-rendering - Any page can be pre-rendered by Next.js, without extra configuration. Pre-rendering entails generating HTML for each page in advance rather than doing it all by client-side JavaScript. This results in better performance and SEO.
• File-system-based routing - Pages in Next.js are associated with a file in the pages directory. Files become routes automatically, removing the need to configure routes manually.
• Rich data fetching methods - Next.js provides getStaticProps and getServerSideProps to fetch data for pre-rendering easily. This data can be used to pre-render pages with the minimal payload required for each page.
• Built-in CSS support - Next.js lets you directly import CSS files for component-level styling. It also handles code splitting for CSS, just like JavaScript.

Client-side rendering (CSR) and server-side rendering (SSR) are two different approaches to sending content to the browser.

JavaScript code then executes on the page, requesting data from the server and dynamically building the complete markup for the page. The browser then renders this markup to display the full page to the user.

JavaScript is primarily used for progressive enhancement and user interactions.

So, CSR relies on client-side JavaScript to assemble page content while SSR renders full pages on the server. The choice depends on the app requirements and priorities around speed, SEO, complexity, and user experience.

This means the initial page content is already present when it loads instead of having empty HTML and waiting for JavaScript to populate it.

Next.js supports two forms of pre-rendering:

1. Static Generation

HTML pages are generated at build time and reused on each request. Pages can be statically generated when the data required to render them is available at build time.

2. Server-side Rendering

HTML pages are generated on each request by the server. Pages are pre-rendered when the data required to render them isn't available during build time.

The key benefits of pre-rendering pages are:

• Better performance - Pages load faster for the user as the content is already present when the page loads. There is no extra latency waiting for JavaScript to fetch data and render the page.
• SEO - Search engines can crawl and index pages better by directly accessing the fully rendered page HTML.
• Initial Load Experience - Users don't see empty loading states when navigating pages. The content is visible right away.

Pre-rendering pages in Next.js combines the performance and SEO benefits of server-side rendering with the benefits of a static site and provides the best possible user experience.

React vs. Next.js: Library vs. Framework

React and Next.js are often compared but serve different purposes. React is a JavaScript library for building user interfaces, while Next.js is a larger framework incorporating React's UI-building capabilities.

The key difference is that React focuses only on the app's view layer - it allows you to create reusable UI components using JSX and React APIs. React is unopinionated, meaning it doesn't make assumptions about other parts of your technology stack.

Next.js, on the other hand, is a complete framework that includes React and additional capabilities like server-side rendering, routing, and page prefetching. Next.js handles more complexity out of the box so that you can build a full-featured web application with fewer dependencies.

Some of the extra functionality provided in Next.js includes:

• File-based Routing: Easy page routing without setting up a separate router.
• Pre-rendering: Automatic page pre-rendering for faster initial loads.
• Code Splitting: Next.js splits code into smaller bundles to optimize performance.
• API Routes: Easily create backend APIs and connect them to front-end routes.
• Image Optimization: Automatic image loading and optimization to improve speed.
• SSR & SSG: Options for both server-side rendering and static site generation.
• TypeScript Support: Native TypeScript integration with no extra configuration.

While React focuses solely on elegant UI code, Next.js incorporates React alongside routing, server-side rendering, optimization, and more out-of-the-box capabilities. This allows Next.js to provide a fully featured framework on top of React's UI foundation.

How React and CSR Work

React is a JavaScript library developed by Facebook for building user interfaces. With React, the application logic is broken down into reusable components that manage their own state and render UI independently.

React uses a declarative paradigm that makes coding complex UIs simpler. Developers describe what the UI should look like under any given state, and React automatically handles rendering it efficiently using a virtual DOM.

Some key aspects of how React works:

• React handles UI rendering - React components contain code that describes how the component should look. When the state changes, React updates the DOM efficiently.
• Interacts with DOM via Virtual DOM - React keeps a lightweight virtual representation of the real DOM. When changes occur, React compares the virtual DOM with the real DOM and only updates what needs changing. This process is faster than manipulating the real DOM directly.
• Data flows down uni-directionally - React follows a top-down uni-directional data flow between components. Parent components pass data to children via props, and children notify parents of any events via callbacks. This makes the app more predictable and more accessible to debug.

In summary, React handles view layer rendering efficiently through its use of a virtual DOM. Components drive the UI, while data flows down uni-directionally between them. This declarative paradigm allows developers to build complex UIs by composing simple reusable components.

How Next.js and SSR Work

Next.js handles server-side rendering for React applications. This means it takes React components and generates static HTML pages on the server at build time. These static pages can then be served quickly and efficiently to the client without depending on client-side JavaScript.

When a Next.js app loads, it sends the rendered HTML from the server to the browser. This allows the page to load incredibly quickly and become interactive, even before all the JavaScript has been downloaded, parsed, and executed.

Once the JavaScript loads, Next.js will hydrate the static HTML with React on the client side. This process converts the static HTML into React components that can then make API calls, handle user events, etc. Hydration allows the benefits of server-side rendering to be combined with the interactive capabilities of React.

In summary, Next.js handles:

• Server-side rendering - HTML is generated on the server
• Fast initial page load - Serving static HTML
• Client-side hydration - Converting HTML to React

This powerful combination allows sites built with Next.js to load instantly with SEO-friendly, static content and then enrich the page interactively on the client side once fully loaded.

React Advantages

React has several key advantages that have made it one of the most popular JavaScript libraries for building user interfaces:

1. Simple & Flexible

One of React's standout features is its simplicity. React uses a declarative paradigm that makes code predictable and easy to understand. The React philosophy is to have small, reusable components with clear responsibilities.

This makes it simple to build complex UIs out of simple building blocks. React components encapsulate markup and logic in one place rather than separating them. This makes it flexible to achieve the component structure you need.

2. Great for Complex UIs

React is especially good for building complex, interactive user interfaces. Its component architecture and the Virtual DOM make React very performant. The Virtual DOM batches DOM changes for efficiency.

These composable components and one-way data flow make React suitable for data-intensive, high-traffic web and mobile apps. Large companies like Facebook, Netflix, and Airbnb use React for complex UIs.

3. Huge Ecosystem

React has a massive ecosystem of open-source libraries and tools. This includes routing, state management, UI component libraries, developer tools, and more. Popular ones include React Router, Redux, Material-UI, and React DevTools.

This rich ecosystem allows developers to quickly build React apps without reinventing the wheel. The React community is very active in creating and maintaining these tools.

React Disadvantages

React is great for building interactive UI components and complex front-end applications. However, as with any technology, React comes with some downsides:

1. Only Handles UI

React focuses solely on the view layer. While it can be combined with other libraries and frameworks, React is not a full-stack solution. It would help if you chose other technologies to handle routing, state management, backend API integration, etc.

2. Setup Can Be Complex

Configuring a React project from scratch requires making many decisions around build tools, module bundlers, state management, routing, and more. While starter kits like Create React App help simplify setup, custom React configurations can be complex.

3. Poor SEO Without Server-Side Rendering

By default, React applications utilize client-side rendering. This means the initial HTML sent to the browser is empty, and JavaScript must execute before the UI is displayed. As search engine crawlers do not run JS, this can negatively impact SEO. Server-side rendering is required for the best SEO with React.

Next.js Advantages

Next.js offers some key advantages over React:

1. Server-Side Rendering for SEO

Next.js pre-renders pages on the server before sending them to the client. This allows search engines to crawl and index the pages for better SEO, unlike a traditional React app, which relies on client-side JavaScript rendering. Pre-rendering in Next.js improves the SEO of landing pages in particular.

2. Easy Routing & Page Management

Next.js provides file-system-based routing and easy page management. Pages are considered separate components in their own right. To create a new page you create a JS file under the pages directory, and the path will match the filename.

Next.js handles all the routing automatically. This avoids manually setting up React Router and configuring all your app's routes.

3. UI Remains in React

Although Next.js handles routing and server-side rendering, the UI remains defined using React components and JSX. Developers can build the UI using React as they usually would. Next.js extends React apps with SSR capabilities while maintaining the React workflow.

Next.js Disadvantages

While Next.js offers many benefits, it also comes with some disadvantages compared to using React alone:

• Additional learning curve. Next.js has its own project structure, routing system, and various APIs that developers need to learn. This adds complexity compared to just using React and its ecosystem. Developers familiar with React will need time to get up to speed on Next.js concepts.
• More complex build setup. Configuring a Next.js app requires Webpack, Babel, and other tools. The Next.js team has made progress in simplifying the setup, but it's still more involved than a basic React app. Some developers prefer the flexibility of setting up their projects without being tied to Next.js conventions.
• Less flexibility than React. Since Next.js has opinions on project structure, routing, styling, and more, developers have less control than React directly. While Next.js is extendable, developers must work within its framework rather than customizing every aspect like with React.

When to Use React?

React is a good choice when you need a simple UI without much complexity. Since React focuses mainly on the view layer, it can be easier to reason about the UI when no state management is required across components.

React is also a good choice if SEO is not a significant concern. Because React uses client-side rendering by default, content is not initially available to search engine crawlers. This makes React well-suited for web apps focused on user interactions rather than SEO.

Additionally, React offers maximum flexibility and control over the app architecture. With React, you are responsible for all the choices - how routing is handled, which state management solution to use, how data is fetched, etc. This flexibility allows tailoring things precisely to your needs but also requires more architectural decisions upfront.

When to Use Next.js?

Next.js is the better choice when:

1. SEO is essential - Next.js offers excellent SEO right out of the box through server-side rendering. Pages are pre-rendered on the server so search engines can crawl them easily. This results in better SEO than a traditional React app.
2. You want easier routing/page management - Next.js simplifies routing and page structure with its file-based routing approach. You can create pages by creating a React component in the pages directory. Next.js handles all the routing for you. This is easier than configuring routers like React Router in a React app.
3. You need a faster initial load - In a React app, the initial load can be slow since the entire bundle needs to be downloaded before rendering. With Next.js's server-side rendering, pages are pre-rendered, so the initial load is much faster. Users don't have to stare at a blank loading screen. The interactivity comes after hydration. So, Next.js is excellent for sites that need quick first-load times.

In summary, if SEO, easier routing, and fast initial loading are important, Next.js is likely the better choice over regular React. The tradeoff is increased complexity, but the benefits outweigh the costs for many apps.

Will Next Replace React?

Though Next.js depends on React for its core UI rendering, it's gaining popularity as a framework for server-side rendered React apps. However, React will likely remain the core UI library for the foreseeable future.

Next.js wraps React and provides an all-in-one framework for building server-rendered React applications. Under the hood, Next still uses React for handling UI components and rendering. So React provides the foundation that Next builds on top of.

However, Next.js handles routing, server-side rendering, static site generation, and other functionality out of the box. This makes it appealing for developers looking for a robust framework for React apps versus using React alone.

So, while Next has yet to replace React, it has become a popular alternative if you need SSR, static generation, and other features it provides. Many developers are choosing Next over sticking with React only these days.

Still, React has a strong foothold as the leading UI library. It will likely continue to power front-end frameworks like Next.js for the long term, even as Next grows in usage. Next, it relies on React to handle core UI rendering tasks.