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The Best Styles in 2024: CSS Modules vs CSS-in-JS

When it comes to styling modern web applications, developers often find themselves choosing between CSS Modules and CSS-in-JS, or in other words, css modules vs css in js. Each approach offers distinct advantages and could significantly impact your project’s architecture and maintainability. Navigating this decision requires understanding their differences, especially how they affect performance and developer workflow. In this guide, we’ll dissect both, css modules vs css-in-js, providing you with the insights needed to make an informed choice for your web development needs.

Key Takeaways

  • CSS Modules provide locally scoped class names with a structured and maintainable approach, integrating well with current CSS tools and pre-processors, yet they may increase bundle sizes and lack built-in support for nested selectors.

  • CSS-in-JS offers the ability to write styles directly in JavaScript, supporting dynamic styling with automatic vendor prefixing and local scoping, but it can lead to larger bundle sizes, potential performance impacts, and requires developers to learn new patterns and possibly syntaxes.

  • Both CSS Modules and CSS-in-JS promote encapsulation of styles within components and have support for dynamic styles and integration with frameworks, yet they differ in performance implications, developer experience, and how they handle theming and advanced features.

But before we begin, here’s a cool interview on what the founder of CSS has to say about CSS-in-JS:

Understanding CSS Modules and CSS-in-JS

Illustration of CSS Modules and CSS-in-JS

In the bustling world of web development, CSS Modules and CSS-in-JS provide developers with powerful tools to handle styling. CSS Modules promote a component-based design with local scope of styles, preventing global conflicts. On the other hand, CSS-in-JS allows developers to write styles declaratively and reusably in JavaScript, bringing a new dimension to styling. Thoroughly exploring the specifics of each approach will help determine which is more suitable for your project.

CSS Modules Explained

CSS Modules are a godsend for web developers, offering a structured and maintainable approach to css styles. With CSS Modules, every class name is locally scoped by default, eliminating global conflicts and ensuring that styles are applied precisely where needed. This approach also streamlines development by integrating with existing CSS tools like css preprocessor support and linters, as well as atomic css, ensuring a smooth and consistent development process. By utilizing css code in a css file, developers can create more efficient and organized projects with the help of a css module.

However, every silver lining has a cloud. With CSS Modules, larger bundles are a reality, and the absence of built-in support for nested selectors may disrupt the development flow. Still, for teams with dedicated markup developers, CSS Modules provide a distinct advantage by keeping styles separate from JavaScript code, enhancing maintainability.

CSS-in-JS: The Basics

CSS-in-JS was a game-changer when introduced in 2015, allowing developers to write styles in JavaScript. Libraries like styled-components further enhanced this approach by enabling the definition of CSS properties within JavaScript, popularizing its use with frontend libraries such as React. As a prominent css in js library, CSS-in-JS provides local scoping of style rules and automatic generation of browser-specific style extensions, offering a fresh perspective on styling vs css in js.

However, despite its advantages, CSS-in-JS presents certain challenges. It can be harder to maintain, performs slower as styles are processed alongside JavaScript. Additionally, it lacks the ability to leverage ready-made utility classes and frameworks. But it can be an ideal solution for front-end teams working on both markup and JavaScript, creating components from scratch, or developing modules that need to integrate with other applications.

Confused? Here’s a video explaining what CSS-in-JS is:

Comparing Styling Approaches

Comparison of Styling Approaches

Armed with a fundamental understanding of CSS Modules and CSS-in-JS, we can now compare these two prominent styling tools. We’ll delve into their respective approaches to:

  • separation of concerns

  • initial setup

  • bundle size

  • performance

  • developer experience

to gain a deeper understanding of how they compare.

Scoping and Organization

One of the key areas where CSS Modules and CSS-in-JS differ is in their approach to scoping and organization. Both methodologies encapsulate styles within components, preventing naming conflicts and style bleed to unrelated elements by using locally scoped classes and unique identifiers. This is a significant advantage for large web applications, as it allows styles to be maintained more easily and promotes a clear structure.

CSS Modules, with their .module.css files and a compulsory compilation step with tools like Webpack, not only promote a clear structure and separation from plain css files but also allow integration with plugins for advanced features and better organization. This structured approach makes CSS Modules highly effective in managing styles in large applications. Meanwhile, for those looking to further enhance their styling with custom components, PureCode.ai offers an array of CSS custom components ready to be integrated into your project. Discover the possibilities and streamline your development process by visiting PureCode.ai. CSS-in-JS also contributes to scalability through encapsulation. Additionally, the use of external css files and js files can help in maintaining a clean and organized codebase.

Performance Implications

In terms of performance, it’s worth noting that CSS-in-JS libraries can have the following impacts:

  • Increase in web application’s bundle size due to the additional JavaScript needed for styling

  • Slower application rendering times as styles need to be converted into plain CSS and added to the document during component rendering

  • Absence of standalone stylesheets that can be cached, which can also impact performance.

On the other hand, CSS Modules contribute to lighter bundles as they don’t add extra runtime code to handle styling, which can lead to reduced code lines and improved page rendering speed. This is a major performance advantage, especially for larger applications where performance is critical.

Developer Experience

The developer experience is a crucial factor when choosing a styling methodology. Here are some considerations for CSS Modules and CSS-in-JS:

  • CSS Modules may feel more intuitive for developers adept in traditional CSS, but learning CSS-in-JS involves adopting new patterns and possibly a new syntax.

  • Tooling for CSS Modules involves setting up pre-processors and linting tools, which can add to the initial setup time.

  • TypeScript integration requires additional steps.

However, CSS-in-JS tends to enhance the developer experience with intuitive APIs and dynamic styling, although it can lead to boilerplate code, cluttering developer tools like React DevTools. On the other hand, CSS Modules require a disciplined approach to maintain the codebase, similar to using Sass with BEM.

Advanced Features and Flexibility

Dynamic Styles and Interactivity in CSS Modules and CSS-in-JS

With a clear understanding of the basics, it’s now time to explore the advanced features and flexibility of both CSS Modules and CSS-in-JS. We’ll investigate their handling of dynamic styles, theming, and how they integrate with popular JavaScript frameworks and libraries.

Dynamic Styles and Interactivity

Theming and Design Systems in CSS Modules and CSS-in-JS

CSS-in-JS libraries, such as Styled Components and Emotion, offer significant functional flexibility and can incorporate extensive logic within style rules. These libraries empower completely dynamic CSS by leveraging native features in frontend frameworks, like component props and state. With CSS-in-JS, styles can adapt in real-time based on props or state changes, eliminating the need for additional classes or complex CSS selectors.

On the other hand, CSS Modules also support dynamic behavior by using CSS variables and JavaScript to update styles at runtime. This approach encourages consistency and the reuse of styles, facilitating the development of interactive web applications. So, both methodologies, including the css in js approach and vanilla css, provide robust support for dynamic styles and interactivity, albeit in different ways.

Theming and Design Systems

Theming is an integral part of modern web development, and both CSS Modules and CSS-in-JS offer robust support. With CSS Modules, styles can be defined and managed per component with props, especially in React applications. This makes it efficient to manage themes and maintain consistency across a large application.

On the other hand, CSS-in-JS libraries like Styled Components facilitate the establishment of modular styles within design systems by defining CSS properties in JavaScript. This allows developers to create unique class names that prevent naming conflicts, simplifying maintenance and style-related code organization. Hence, both methodologies offer robust theming and design system support but differ in their implementation.

Integration with Frameworks and Libraries

Integration with popular JavaScript frameworks and libraries is a key consideration when choosing a styling methodology. CSS Modules fit well in the component-centric design of React applications, integrating via JavaScript files and the styleName prop to correlate with CSS classes. They can also integrate with Angular and Vue.js, offering a versatile approach to styling.

In contrast, CSS-in-JS libraries such as Radium and Styled JSX are designed to work with specific JavaScript frameworks, adhering to the stylistic conventions of the framework in use. However, framework-agnostic CSS-in-JS libraries such as JSS, Emotion, and Styled Components provide flexibility for use with any component-based framework. This makes CSS-in-JS a versatile choice for a variety of projects.

Real-World Case Studies

Real-World Case Studies of CSS Modules and CSS-in-JS

Having explored the intricate details of CSS Modules and CSS-in-JS, we’ll now turn our attention to some real-world case studies. These instances illuminate the practical use of these methodologies in commercial projects, providing insights into the technical and organizational challenges faced.

Case Study: CSS Modules

Cartogram, a company working on large projects, faced challenges with CSS bloat from legacy code which prompted a move towards CSS Modules. By adopting CSS Modules, Cartogram was able to integrate complex features into their existing code base without disrupting the rest of the project.

The structured approach of CSS Modules allowed styles to be maintained more easily by being specific to their components and located alongside the corresponding functionality and markup. This case study highlights the benefits of CSS Modules in managing legacy code and enhancing maintainability in large projects.

Case Study: CSS-in-JS

On the other hand, a project that adopted CSS-in-JS, such as Spectrum, experienced significant improvements in the ability to write maintainable and scalable styles, compared to using inline styles. Developers at Spectrum found it easier to keep styles isolated and the project benefited from CSS-in-JS’s capacity to leverage JavaScript’s power, facilitating dynamic styling, and adopting theme-based design with ease.

However, there were initial challenges, including a performance hit due to added runtime dependency and heavier initial load times. Developers also had to overcome a learning curve to effectively utilize CSS-in-JS. Despite these challenges, the long-term benefits in maintainability and developer agility justified the switch.

Making the Right Choice for Your Project

Your project requirements and team structure should inform the choice between CSS Modules and CSS-in-JS. CSS Modules are well-suited for complex UIs and performance-critical applications, while CSS-in-JS may be more appropriate for applications where performance is less of a priority or for those that require robust design systems.

Adopting CSS Modules can modernize a project and set the stage for future updates, thereby ensuring long-term maintainability and scalability. But ultimately, the choice depends on your team’s capabilities and your project’s specific needs.

Informed Decision-Making: CSS Modules vs CSS-in-JS

The journey through the world of CSS Modules and CSS-in-JS has been enlightening. We’ve explored the origins, strengths, and weaknesses of both methodologies, compared them in terms of scoping, performance, and developer experience, and examined their advanced features and flexibility.

In conclusion, both CSS Modules and CSS-in-JS offer powerful solutions to the challenges of modern web development. While CSS Modules provide a structured and maintainable approach to styling, CSS-in-JS brings dynamic styling capabilities and easier theming. The choice between the two ultimately depends on the specific requirements of your project and the capabilities of your team. If you’re looking to further enhance your styling practices, consider exploring PureCode.ai for an array of CSS custom components ready to be integrated into your project. So, the next time you embark on a web development project, which will you choose?

Frequently Asked Questions

What is the difference between CSS and CSS module?

The main difference between CSS and CSS Module is that CSS Modules scope class names and animation names locally by default, while normal CSS files apply styles globally. This means that with CSS Modules, style definitions are scoped to specific components rather than being global.

Why we stopped using CSS-in-JS?

We stopped using CSS-in-JS because it increases bundle size, clutters React DevTools, and may negatively impact performance, especially with SSR and component libraries. This is due to the insertion of new style rules at runtime.

Is CSS-in-JS better than CSS?

Both CSS-in-JS and CSS Modules have their proponents, with CSS-in-JS appealing to developers who favor JavaScript for styling and CSS Modules being preferred by those who value support for both developers and end users in current technologies.

What are the main differences between CSS Modules and CSS-in-JS?

In conclusion, CSS Modules promote a component-based design with local scope of styles, while CSS-in-JS enables developers to write styles in JavaScript—a shift that may require adapting to new patterns and syntax.

Andrea Chen

Andrea Chen