Comparison of Styled Components vs CSS Modules: Performance, Use Cases, Trends

Choosing the right styling solution for your React project can be somewhat challenging. So in this post, we'll dive deep into a comparison of CSS Modules vs Styled Components, exploring their performance, ease of use, and best use cases.

Whether you're optimizing for speed or looking for flexible styling, understanding these tools will help you make an informed decision. Let's break down their pros and cons to see which fits your project best.

Interested in other detailed comparisons of CSS frameworks? 📖

What are CSS Modules?

CSS Modules are a way to scope CSS by automatically generating unique class names. This prevents style conflicts in large applications. Each component gets its own CSS file, ensuring styles are locally scoped by default.

Benefits and Common Use Cases

1. Scoped Styles: CSS Modules ensure styles are specific to the component, reducing the risk of conflicts.

2. Maintainability: Easier to maintain and understand in large codebases.

3. Compatibility: Works well with existing CSS and preprocessors like SASS.

4. Use Cases: Ideal for large-scale applications where style encapsulation is critical, such as complex web apps and multi-developer projects.

What Are Styled Components?

Styled Components is a library for React that allows you to use component-level styles in your application. It leverages tagged template literals to style your components, keeping JavaScript and CSS in the same file.

Benefits and Common Use Cases

1. Dynamic Styling: Enables styles to be tied directly to component logic, allowing for dynamic styling based on props and state.

2. CSS Syntax: Uses familiar CSS syntax within JavaScript, making it easy for developers with CSS knowledge to adapt.

3. Enhanced Developer Experience: Provides a better development experience with features like automatic vendor prefixing and easier theming.

4. Use Cases: Perfect for projects needing dynamic styles or themes, like design systems and modern web applications where components often change styles based on user interaction or state.

The Problem of Style Cascading: How both solutions address the issue

With traditional CSS, style rules can cascade and affect elements unintentionally, leading to style conflicts and unexpected behavior. Both Styled Components and CSS Modules address this problem. Styled Components leverage JavaScript to inject styles dynamically, limiting the scope and reducing the likelihood of style collisions. CSS Modules take a different approach by scoping each style to a specific component, using unique class names that avoid undesired cascading.

Atomicity, reusability, and side effects: How Styled Components and CSS Modules handle these

Styled Components and CSS Modules both offer solutions to achieve atomicity, the principle of creating small, independent units of style that are easy to understand, test, and reuse. Styled Components does this by bundling CSS with JavaScript, allowing developers to create reusable, atomic component styles. CSS Modules, on the other hand, uses a similar approach but isolates CSS from JavaScript, helping to control side effects and improve reusability.

With the rise of Headless Content Management Systems (CMS) like Caisy, these styling solutions become even more useful.

👉 A Headless CMS separates the frontend presentation layer from the backend, providing greater flexibility and control over how content is displayed. This separation makes managing styles crucial to maintain a consistent user experience across different platforms. Read a more detailed explanation of headless CMS to fully understand the architecture.

Advantages of CSS Modules

1. Scoped Styles: CSS Modules automatically scope class names to avoid conflicts, ensuring that styles are applied only to specific components. This makes it easier to manage and maintain styles, especially in large projects.

2. Simplicity and Compatibility: They use standard CSS syntax, which means developers don’t need to learn new syntax. They also work well with CSS preprocessors like SASS, making integration into existing projects straightforward.

3. Performance: Since CSS Modules generate static class names, they can be more performant than dynamic solutions like CSS-in-JS. The styles are processed at build time, resulting in smaller, more optimized CSS files.

4. Tooling Support: CSS Modules have wide support in most modern build tools and frameworks, such as Webpack and Next.js. This makes setup and integration smooth and efficient.

Cons of CSS Modules

1. Limited Dynamic Styling: CSS Modules are less flexible for dynamic styling based on component state or props compared to CSS-in-JS solutions.

2. Verbose Class Management: Managing and importing class names can become verbose and cumbersome, especially when dealing with complex styles or many components.

3. Lack of Advanced Features: They don’t provide some advanced features out of the box, like automatic vendor prefixing or theme support, which may require additional tools or configurations.

Pros of Styled Components

1. Dynamic Styling: Styled Components allow for dynamic styles based on props, state, or theme. This is particularly useful for building highly interactive applications where the styles need to change frequently based on user interaction or data​.

2. Component-Level Styles: Styles are written in JavaScript and scoped to the component, ensuring that each component’s styles are encapsulated and easy to manage.

3. Enhanced Developer Experience: Features like automatic vendor prefixing, theming support, and a cohesive developer experience within the JavaScript ecosystem make Styled Components a pleasure to work with. Tools like the styled-components Babel plugin can also improve performance by transforming styles at build time.

4. CSS Syntax: Styled Components use familiar CSS syntax within JavaScript, making it easy for developers with a background in CSS to adapt.

Styled Components Weaknesses

1. Performance Overhead: Styled Components can introduce runtime performance overhead since styles are generated on the fly. This can be mitigated with tools like the Babel plugin, but it’s something to consider for performance-critical applications​ (Qwik)​.

2. Learning Curve: While the CSS syntax is familiar, the concept of writing styles within JavaScript and using tagged template literals can take some time for new developers to get used to.

3. Build Size: Including Styled Components in your project can increase the bundle size due to the additional JavaScript required for styling logic. This can affect load times and overall performance if not managed properly.

By weighing these pros and cons, you can make an informed decision on whether Styled Components vs CSS Modules is the better fit for your project.

Load Times File Sizes and Runtime Performance 🚀

CSS Modules typically result in smaller and more optimized CSS files because styles are statically generated at build time. This reduces the overall load time and file size, which can be beneficial for large applications that require quick load times and minimal data transfer​​.

Styled Components, while offering great flexibility and dynamic styling, introduce a runtime performance overhead. This is due to the fact that styles are generated on the fly within the JavaScript runtime. However, tools like the babel-plugin-styled-components can optimize this process by transforming styles at build time, reducing the impact on runtime performance​ (LogRocket Blog)​.

Real-World Benchmarks

In real-world applications, CSS Modules often outperform Styled Components in terms of initial load times and bundle size. For instance, a study showed that projects using CSS Modules had smaller JavaScript and CSS bundle sizes compared to those using Styled Components. This is crucial for performance-critical applications where every byte counts​.

Caching and SSR (Server-Side Rendering)

Styled Components support server-side rendering (SSR) out of the box, which can improve initial render performance and SEO. CSS Modules also support SSR but may require more configuration. Both methods can benefit from effective caching strategies to enhance performance further. However, dynamically generated styles in Styled Components can sometimes hinder caching efficiency​.

Bundle size comparison: What’s causing the difference?

An important aspect to consider when developing apps is the impact on bundle size. The file size of CSS Modules tends to be smaller than that of styled-components. This can largely be attributed to the extra code that styled-components adds for runtime handling and styling of the head section. When replacing styled-components with CSS Modules, developers often found an improvement in bundle size and runtime performance.

/* Bundle size impact */
// With styled-components
webpack-bundle-analyzer bundle.js

// Total Size: 1.2M

// With CSS Modules
webpack-bundle-analyzer bundle.js

// Total Size: 950K

Conclusion

So let's sum up this performance comparison: CSS Modules generally offer better performance in terms of load times and file sizes, making them suitable for large-size and performance-critical applications. Styled Components, on the other hand, provide superior flexibility for dynamic styling, which can justify their use in projects that require frequent style changes based on user interactions or state. The choice between the two should be based on the specific needs of the project, balancing performance with styling flexibility.

Effects of CSS Modules on SEO

CSS Modules can positively affect SEO by optimizing load times and ensuring styles are correctly applied without conflicts. Since CSS Modules generate static CSS files, they are included in the initial HTML payload, making styles available as soon as the HTML is parsed. This can improve the time to first paint (TTFP) and reduce cumulative layout shift (CLS), both of which are important metrics for SEO​.

Learn about further CSS Rules for SEO.

Additionally, CSS Modules avoid the need for JavaScript to parse and apply styles at runtime, which can further enhance page speed—a critical factor in search engine rankings. By keeping styles scoped and minimal, CSS Modules help in maintaining a lean and efficient codebase, leading to optimized site speed and improved SEO​.

Styled Components and SEO

Styled Components offer dynamic and flexible styling, but this comes with certain SEO considerations. Because Styled Components generate styles at runtime within JavaScript, there can be a delay in applying styles until JavaScript execution is complete. This can negatively impact the largest contentful paint (LCP) and other performance metrics, potentially affecting SEO rankings​​.

However, Styled Components support server-side rendering (SSR), which can mitigate some of these issues by ensuring styles are available as soon as the HTML is loaded. SSR helps improve initial load times and enhances the overall user experience, contributing positively to SEO. It’s essential to properly configure SSR and caching strategies to balance the flexibility of Styled Components with the need for performance optimization​.

To not lose track of your SEO results, make sure to use tools like Google Analytics and GTM.

Implementing CSS Modules in React

Step-by-Step Tutorial

1. Setup Your React Project:

   npx create-react-app my-app
   cd my-app

   
   

2. Create a CSS Module File:

   In your src folder, create a new file Button.module.css:

   .button {
     background-color: blue;
     color: white;
     border: none;
     padding: 10px 20px;
     cursor: pointer;
   }

   
   

3. Import and Use the CSS Module in a Component:

   Create a Button.js file in the src folder:

   import React from 'react';
   import styles from './Button.module.css';
   
   const Button = () => {
     return <button className={styles.button}>Click Me</button>;
   };
   
   export default Button;
   

   
   

4. Render the Component:

   Update App.js to include the Button component:

   import React from 'react';
   import Button from './Button';
   
   function App() {
     return (
       <div className="App">
         <Button />
       </div>
     );
   }
   
   export default App;

   
   

Sample Code Snippets:

/* Button.module.css */
.button {
  background-color: blue;
  color: white;
  border: none;
  padding: 10px 20px;
  cursor: pointer;
}

// Button.js
import React from 'react';
import styles from './Button.module.css';

const Button = () => {
  return <button className={styles.button}>Click Me</button>;
};

export default Button;

How to Implement Styled Components in React

Step-by-Step Tutorial

1. Setup Your React Project:

   npx create-react-app my-app
   cd my-app

   
   

2. Install Styled Components:

   npm install styled-components

   
   

3. Create a Styled Component:
   Create a Button.js file in the src folder:

   import React from 'react';
   import styled from 'styled-components';
   
   const StyledButton = styled.button`
     background-color: blue;
     color: white;
     border: none;
     padding: 10px 20px;
     cursor: pointer;
   
     &:hover {
       background-color: darkblue;
     }
   `;
   
   const Button = () => {
     return <StyledButton>Click Me</StyledButton>;
   };
   
   export default Button;

   
   

4. Render the Component:

   Update App.js to include the Button component:

   import React from 'react';
   import Button from './Button';
   
   function App() {
     return (
       <div className="App">
         <Button />
       </div>
     );
   }
   
   export default App;

   
   

Sample Code Snippets:

// Button.js
import React from 'react';
import styled from 'styled-components';

const StyledButton = styled.button`
  background-color: blue;
  color: white;
  border: none;
  padding: 10px 20px;
  cursor: pointer;

  &:hover {
    background-color: darkblue;
  }
`;

const Button = () => {
  return <StyledButton>Click Me</StyledButton>;
};

export default Button;

By following these tutorials, you can effectively implement both CSS Modules and Styled Components in your React projects, each offering unique advantages.

Common Pitfalls and How to Avoid Them

One common pitfall is the incorrect use of Styled Components. This can result in namespace conflicts and adversely affect HTML tags. To avoid it, some developers recommend using Styled Components only for the page box and using CSS classes for the rest of the styling. This approach gives better control over the namespace and HTML tags as CSS classes are kept from interfering with each other.

Using both Styled Components and CSS Modules simultaneously is not common, but it's not necessarily wrong either. It's advisable to understand the unique benefits of both before deciding to use them concurrently.

How User Experience Is Affected by the Choice of CSS Styling

The challenge that both Styled Components and CSS Modules share is the need to provide a smooth user experience while writing meaningful and maintainable code. CSS Modules require non-standard CSS syntax and the need to include styles when integrating into a project. Additionally, CSS Modules result in a smaller file size compared to their JS counterparts, leading to potentially quicker load times and an improved user experience.

On the other hand, Styled Components allow the use of normal HTML attributes and JavaScript, which lends itself to a more developer-friendly experience. However, they can increase the runtime and the bundle size, which could degrade performance and adversely affect the user experience.

Despite these differences, both Styled Components and CSS Modules aim to address the same problems: style cascading, atomicity, and reusability.

Ultimately all tech choices should come down to the individual project requirements. After reading this comparison of CSS Modules vs Styled Components, think about your skills, project goals and needs. Both ways have their unique advantages and challenges, which you're now familiar with. What you make out of this information, is up to you. 😃

With this in mind, consider adding a Headless CMS Solution like Caisy to your tech stack. Caisy is a high-performing CMS and one of the best tools for developers. The flexible and scalable system is built to support popular web frameworks such as Next.js, Nuxt, Svelte, and Astro.

Caisy aligns perfectly with the need for a sleek, fast, and friendly interface that supports complex designs. If the journey of development has taught us anything, it is the constant need for adaptability and the right toolset. The CMS mirrors these principles in its functionality, making it a compelling choice regardless of your chosen CSS styling approach.

So why wait? See it for yourself!

Create your free Caisy account today or get a personal tour through the system in a Headless CMS Demo Call.