Issues with NextJs 14.2 (app router) and global scss file

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04-10-2024

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Next.js 14.2 and the Great Global SCSS Mystery: A Guide to Solving the Problem

Next.js 14.2 introduced the App Router, a game-changer for building dynamic user interfaces. However, with great power comes the need for careful navigation, especially when it comes to integrating global CSS stylesheets, like those written in SCSS. This article will guide you through the common problems you might encounter and provide practical solutions.

The Scenario

Imagine you have a shiny new Next.js 14.2 project. You want to use a single SCSS file for global styles across your application. You might write your SCSS file (e.g., global.scss) and import it into your app/layout.js file:

import '../styles/global.scss';

You're expecting your global styles to apply beautifully to all pages, but they're either not loading or causing unexpected behavior. This is where the "great global SCSS mystery" begins.

The Root of the Problem

The issue lies in the way Next.js 14.2 handles styles within the App Router. The app/layout.js file defines a new "client-side" layout context. While this offers improved performance, it also introduces a potential conflict when it comes to loading styles:

• Server-side (Static Generation): During initial rendering (server-side), styles are applied to your components.
• Client-side (Hydration): After hydration (when the client takes over rendering), styles might be applied differently, or not at all, depending on how your SCSS file is imported.

Solutions for a Seamless Stylistic Experience

Here's how to ensure your global SCSS file works flawlessly with Next.js 14.2:

1. Use global.css for Basic Styles:

   For simple, global styles that don't require advanced features like variables or mixins, consider creating a global.css file and importing it directly into your app/layout.js:

   import '../styles/global.css';
   

   This ensures the styles are applied correctly on both the server and client.

2. Leverage @import and Separate Components:

   If you need more complex SCSS features, use @import to break down your global styles into component-specific files:

   // global.scss
   @import './header.scss';
   @import './footer.scss'; 
   
   // header.scss
   .header { 
       // Header styles
   }
   
   // footer.scss
   .footer { 
       // Footer styles
   }
   

   Then, import each component-specific SCSS file into the relevant component layout file (e.g., app/layout.js or app/page.js).

3. Adopt CSS Modules:

   CSS Modules provide a powerful way to manage styles by creating unique class names and avoiding conflicts. This approach might require some adjustments to your existing code, but it ensures cleaner separation and better predictability:

   // MyComponent.module.scss
   .container {
      background-color: #f0f0f0;
   }
   

   In your component:

   import styles from './MyComponent.module.scss';
   
   function MyComponent() {
     return <div className={styles.container}>My Component</div>;
   }
   

Key Takeaways

• Understanding Client-Side Hydration: The App Router's client-side hydration is crucial for performance, but it can affect how styles are applied.
• Modularization is Your Friend: Break down your SCSS into component-specific files to maintain better organization and prevent conflicts.
• Explore CSS Modules: Consider using CSS Modules for greater control and predictability, especially for large projects.

References

• Next.js Documentation: App Router
• CSS Modules: Next.js
• Understanding CSS Modules

Remember: Always test your styles across different browsers and devices to ensure a consistent user experience. Happy styling!