Probably one of the most important decisions you'll make while building an app is how you are going to style your components. The two popular techniques in terms of CSS are the use of CSS in JS and Traditional CSS. Each technique can have some benefits or drawbacks in a specific context or when certain features are needed. In this blog post, let's compare the two methodologies, figure out what their pros and cons are, and how we can decide which fits better in our project.

Let’s talk about Traditional CSS first…

What is Traditional CSS?

Overview

Traditional CSS is the classic way of styling web pages using external .css files. The styles are written in a separate file and linked to HTML or JavaScript files. Traditional CSS is often written using pre-processors like Sass or Less and utilizes cascading rules to apply styles globally.

Advantages of Traditional CSS

• Separation of Concerns: CSS in separate files keeps the structure (HTML), behavior (JavaScript), and styling (CSS) distinct, making the code modular and organized.

• Global Styles: Traditional CSS allows you to create styles that can be applied across your entire project, which can be a significant benefit for large-scale applications.

• Caching: External CSS files can be cached by the browser, which helps in reducing load times and improving performance.

• Familiarity and Community Support: Traditional CSS has been around for decades, meaning there is widespread community support, documentation, and tools available.

Downsides of Traditional CSS

• Global Namespace Issues: Styles are globally scoped by default, which can lead to name collisions. This can be mitigated using conventions like BEM (Block Element Modifier), but it still requires careful management.

• Difficulty in Managing Large-Scale Projects: As the project grows, maintaining a large CSS codebase can become tricky, with style overrides and specificity wars potentially leading to bugs.

• Lack of Dynamic Behavior: Traditional CSS lacks native support for dynamic styling based on JavaScript variables or state, often requiring extra classes or inline styles to achieve such effects.

---

What is CSS in JS?

Overview

CSS in JS refers to the practice of writing CSS directly inside your JavaScript files. Instead of maintaining separate .css files, you define your styles within JavaScript objects or templates. This approach is especially popular in modern React and Vue.js applications, where CSS is scoped to individual components. Libraries like Styled-Components, Emotion, and JSS have accelerated the adoption of this pattern.

Advantages of CSS in JS

• Scoped Styles: Styles are encapsulated within components, avoiding global namespace pollution and reducing the likelihood of style conflicts.

• Dynamic Styling: CSS in JS allows you to apply styles conditionally, based on state or props. This makes it easier to create responsive, themeable, and interactive designs.

• Maintainability: Since the styles are co-located with the component logic, it makes maintaining and updating code simpler, especially in component-based libraries like React.

• Dead Code Elimination: Unused styles can be easily identified and eliminated, improving the overall performance of the application.

• Modular and Scalable: Large projects can benefit from the modularity provided by CSS in JS, where each component controls its own styles.

Downsides of CSS in JS

• Performance Overhead: Some CSS-in-JS libraries inject styles dynamically during runtime, which can introduce performance bottlenecks, especially in larger applications.

• Complexity: The learning curve for CSS in JS can be steep for developers unfamiliar with the concept. Managing styles in JavaScript can sometimes lead to more complicated code.

• Tooling and Browser Compatibility: Although most modern browsers support CSS in JS solutions, tooling can be less mature than traditional CSS. It may require more configuration to work seamlessly with older browsers or complex build systems.

• Bundling: CSS in JS often leads to larger JavaScript bundles, which can slow down page load times if not managed properly.

---

Key Differences Between CSS in JS and Traditional CSS

---

Which One Should You Use in Your Project?

When to Choose Traditional CSS

Traditional CSS may be the right choice for your project if:

• You just love simplicity: If you are building a static or low-scale website with non-deep styles, then traditional CSS offers a simple and usual way.

• Performance is a top priority: In this regard, traditional CSS will be a better choice because it is easily cacheable and doesn't have runtime injection.

• You want global styles: Traditional CSS is a good choice if you need to keep a bigger part of your website or application with the same style.

---

When to Choose CSS in JS

CSS in JS might be more suitable if:

• You’re working with React or Vue.js: For component-based frameworks, CSS in JS integrates naturally, improving development efficiency.

• You need dynamic styles: If your application requires complex interactions, such as theming, state-based styling, or responsiveness, CSS in JS allows for seamless, real-time styling changes.

• Maintainability is a concern: For large projects with many components, CSS in JS allows for more modular and scoped styles, reducing the chances of conflicts and making it easier to update styles.

• You need scalability: If your team is working on a long-term project where components need to be easily reused and maintained, CSS in JS offers better scalability through component isolation and reusable styles.

---

Hybrid Approach: Best of Both Worlds?

Many teams opt for a hybrid approach, using CSS in JS for component-level styles and traditional CSS for global styles like typography and layout. In this way, you can have the best of both worlds, utilizing global CSS for performance and scalability along with the benefits of modularity and the dynamic nature of CSS in JS.

---

Conclusion

Both CSS in JS and Traditional CSS have their own merits and challenges, and the decision largely depends on the nature of your project, team expertise, and specific requirements. If you're building a complex, interactive web app with a component-driven architecture, CSS in JS might be a better fit.

On the other hand, if you prefer a familiar, performant, and globally scoped approach, Traditional CSS still has plenty of value.

At the end of the day, your choice should align with the goals and constraints of your project. You need to consider the complexity, performance needs, and long-term maintainability before committing to either option—or explore a hybrid approach for more flexibility.

What’s Your Take?

Which approach do you prefer for your projects? Share your experiences in the comments below!