Styled Components vs CSS Modules

2 February 2024

Styled Components vs CSS Modules

Ed Robinson, Lead Software Engineer

Understanding Styled Components & CSS Modules

Overview of Styled Components and CSS Modules

Styled Components and CSS Modules are popular technologies offering advanced styling capabilities for modern web development. Styled Components, a CSS-in-JS solution, allows developers to use JavaScript logic within styles, creating a more dynamic styling environment. CSS Modules, on the other hand, externalize styling from JavaScript into standard CSS, providing a more traditional approach to web styling.

Both technologies offer unique benefits depending on the specific requirements and context of a project. That's why it is very helpful to understand their differences, how they address cascading style problems, and their approaches to atomicity, reusability, and side effects. So let's dive into the comparison!

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. Headless CMS separate 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. For a more detailed explanation of headless CMS read this guide. Whether using Styled Components or CSS Modules, caisy helps developers manage their styles effectively, adapting to changes in content structure and presentation, and ensuring a seamless integration between frontend design and backend management.

While performance, bundle size, and the specifics of JavaScript usage in Styled Components vs CSS Modules are further topics to be explored in depth in the next sections of this article, this overview gives a solid grounding in understanding what both these technologies offer and how they can significantly enhance style management in modern web development.

Headless CMS for developers

Your terms, your stack. Experience unmatched speed and flexibility with caisy - the headless CMS you've been dreaming of.

A graphic showing caisy's benefits for developers, including frameworks and features.

Key Differences between Styled Components and CSS Modules

In this section, we'll explore some key differences between styled-components and CSS Modules. We'll cover their relationship with JavaScript, impact on bundle size, a real-life use case of swapping these solutions, and their support for different libraries, utilities, and plugins.

Interested in detailed comparisons of CSS frameworks? Click here!

The role of JavaScript in Styled Components vs CSS Modules

In styled-components or CSS-in-JS, the power of JavaScript can be leveraged in styles by injecting JS logic. This can be useful for dynamic styling based on specific conditions. On the other hand, CSS Modules uses a non-standard CSS syntax and doesn't support this feature inherently, but you can still use JavaScript to animate styles or to toggle classes.


/* Styled Component */
const Button = styled.button`
  background-color: ${props => props.primary ? 'blue' : 'green'}
`;

/* CSS Module */
.button {
  composes: primary from global;
}

.primary {
  background-color: blue;
}

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

Swapping the solutions: A look into a use case

When one developer replaced styled-components with CSS modules in their app, they noticed improved runtime performance and a decrease in bundle size. However, they lost the convenience of the API design that styled-components offered. This illustrates that while styled-components have their advantages like prop-based styles and automatic vendor prefixing, the increased bundle size can be a deterrent for some developers.

Support for libraries, utilities, and plugins

Finally, comparing support for different libraries, utilities, and plugins, CSS Modules can be a clear winner for teams already familiar with CSS and its ecosystem. CSS Modules can use SCSS, Less, Postcss, and stylelint.

On the other hand, styled-components have limited support for libraries and plugins and might require additional tooling. However, styled components do provide advantages such as the ability to use JavaScript logic in styles along with states, nesting, and media queries.

/* Styled Component */
const Button = styled.button`
  &:hover {
    background-color: blue;
  }
  
  @media (max-width: 700px) {
    background-color: red;
  }
`;

/* SCSS with CSS Modules */
.button {
  &:hover {
    background-color: blue;
  }
  
  @media (max-width: 700px) {
    background-color: red;
  }
}

Overall, each solution has its strengths and pitfalls and developers should choose based on their specific project needs and team expertise. The next sections will dive deeper into the usage and practical examples of each solution, so continue on to gain a fuller understanding of these powerful tools.

Why Choose Styled Components

In this section, we delve into the edges that styled components have over CSS modules. Styled-components bring various advantages to the table that make them preferable in certain scenarios. However, like every tool, they have limitations that might affect their utility in some instances.

Advantages of using Styled Components over CSS Modules

Styled components handle styles within the JS runtime and append them to the <head> section of your HTML document. These manipulations are conducted without the obstacle of hashed names, an issue which you might encounter with CSS Modules.

Furthermore, styled-components allow developers to utilize JS logic within the styles. This tactic, though unsupported by most libraries, facilitates the integration with small modules. Another edge of styled-components is the support for normal HTML attributes, states, nesting, and media queries. They generate a "real" class attribute and isolate CSS in the head, enabling styling of custom components that only accept the className prop.

Scenarios where styled-components excel

If you have an application where speed is paramount and faster page loads are the end goal, styled-components could be the perfect choice for you. Additionally, web applications that lean heavily on component-based architecture would significantly benefit from styled-components due to the flexibility.

Sharing code between projects with Styled Components

While sharing code between projects can present some difficulty with styled-components, the direct CSS and JavaScript integration they offer makes for an excellent tool for projects requiring a more modern styling approach.

Limitations of Styled Components

Despite their many advantages, styled-components do have a few limitations. They contribute to a larger bundle size, partly due to the additional code that is necessary to append styles to the <head> section. Additionally, this CSS-in-JS approach is less suitable when you have a dedicated individual working on markup and when there is a need for ready-made approaches and utilities. Lastly, unlike with CSS Modules, stylelint and SCSS support are unavailable with styled-components.

In conclusion, like every tool, styled-components and CSS Modules both have their strengths and constraints. The choice largely depends on the unique needs of your specific project.

The Power of CSS Modules

Benefits of using CSS Modules

CSS Modules offer several key advantages for developers focusing on maintainability and clean code. As one of these benefits, CSS Modules use a hash-based transformation of style names based on factors such as the filename, path, and style name. This approach minimizes the chances of class name collisions and enhances the reusability of components.

Furthermore, the ability to work with regular CSS and use CSS pre-processors and utilities with CSS Modules contributes to clean, clearly organized code and a standardized approach. Even with the exception of global styles, the syntax and structure are familiar to developers with CSS experience.

Instances where CSS Modules reign supreme

In terms of bundle size, there is a clear advantage to using CSS Modules over styled-components. As a result, you might see performance improvements and reduced bundle size when migrating to CSS Modules. Therefore, for projects that require optimized loading speed and performance, using CSS Modules could be the better choice.

However, several other circumstances also make CSS Modules shine. For projects with a dedicated person working on the markup, or when ready-made approaches and utilities are required, CSS Modules offer an optimal solution. They also provide an efficient way of sharing code between multiple projects.

Drawbacks of using CSS Modules

Like every other technology, CSS Modules have their drawbacks. The main shortcoming is that most libraries don't support the integration of JS logic into styles, a situation that limits the use of dynamic styling.

Another limitation of CSS Modules is the difficulty with handling global styles. Whilst scoped styles contribute to modularity and cleanliness of the code, global styles might be more complex to implement.

Finally, you might encounter a lack of basic features that are readily available in modern styling libraries, such as support for states, nesting, and media queries. Keep in mind that if you're prioritizing these features, CSS Modules might not be the best choice. However, alternating solutions like Linaria, offering similar API design to Styled Components with the runtime removed, could be explored.

Practical Use-cases and Examples

There are several practical use-cases and real-world examples when it comes to choosing between Styled Components and CSS Modules.

Styled Components vs CSS Modules in Real-World Projects

The macos.now.sh project originally utilized Styled Components for ease of component-based styling in React. Styles were easily written in a familiar format and props could be passed dynamically to influence styles. However, due to performance considerations, they switched to CSS Modules, which treats styles as scoped, separate CSS files associated with their respective components. One of the major benefits of this switch was improved runtime performance and reduced bundle size. However, the loss of the API design of Styled Components and the convenience of writing styles in JavaScript was a drawback of this switch.

Another example involves the use of Linaria, another CSS-in-JS library similar to Styled Components. Linaria was used as it offers the same API as Styled Components but extracts the CSS into separate files during the build, which can significantly improve performance.

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 this, 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.

Performance Examination: Styled Components vs CSS Modules

Evaluating and Comparing the Performance Metrics

Comparing the performance between styled components and CSS modules requires a detailed understanding of how each approach impacts the build size and runtime of a web application. A comparative study, mentioned in an article on dev.to, indicates that CSS Modules tend to outperform styled-components in terms of build size. This implies that, for large-scale web applications where reduced bundle size is a priority, CSS Modules could offer superior performance. On the other hand, the speed benefits that come with using JavaScript logic (if you opt for styled-components) could compensate for the increased build size. However, such benefits would highly depend on the complexity and requirements of your application.

Effect on Webpage Performance and Alternatives for Styling

The impact of using different styling techniques, such as styled components or CSS Modules, on webpage performance is a crucial aspect that may not be always straightforward to assess. As stated in a blog post on pustelto.com, real-world performance comparisons between such methods are franky scarce.

The author of the aforementioned blog has carried out a performance test using Linaria, a runtime CSS-in-JS library. The observations of this test showed that replacing styled-components with Linaria resulted in fewer total requests and a smaller bundle of CSS and JavaScript sizes. Moreover, Linaria outperformed in terms of various Web Vitals metrics and presented a decrease in time spent on scripting and lower total blocking time.

As a developer, it's valuable to consider these impacts when deciding on your preferred styling method for your React applications and perhaps even lean towards alternatives like build-time CSS-in-JS libraries or perhaps conventional CSS.

Optimizing for Speed: How to Choose based on Performance

Accommodating for speed in a web application is pivotal and the styling tools can greatly influence it. According to a Stack Overflow post, using glamorous or styled-components can be advantageous in terms of rendering speed. Still, challenges such as sharing code across multiple projects can be more difficult when styled-components are your go-to.

On the other hand, options like SASS/CSS and inline styles might deliver more speed although not providing the added flexibilities of components like styled-components. Therefore, the ultimate decision around which method to use for your styling needs should consider not just the speed but also factors like scalability, readability, ease of maintain, and commensurability with your codebase.

In conclusion, performance metrics are an important decision criterion for choosing between styled-components and CSS Modules, but the trade-offs with other needs of your application should always be considered.

Community reviews on Styled Components and CSS Modules

Developers often view the choice between Styled Components and CSS Modules through the lens of application size and team makeup. For smaller applications, with a single team, CSS Modules have reportedly been the preferred choice. Styled Components, on the other hand, have been found to be more suitable for frontend teams, working both on markup and JavaScript, developing components from scratch, or integrating modules into other apps.

However, each of these tools has its own pros and cons. Styled Components, being CSS-in-JS based, provide more flexibility and development ease for small modules. But they fall short when it comes to rendering speed, cacheability, library support and integration. CSS Modules uses a non-standard syntax for global styles, includes styles during project integration, and requires generating interfaces when using TypeScript. But on the upside, they allow the use of standard CSS and utilities.

Popular opinions on performance, usability, and other factors

A key factor developers weigh while choosing the right styling tool is bundle size. Synthetic tests have shown CSS Modules result in a smaller bundle size compared to Styled Components. This feature often sways decisions towards CSS Modules, to ensure optimized performance.

On usability, developers value the API design and convenience provided by Styled Components. They appreciate being able to write normal HTML attributes, mix in JavaScript, support for states, nesting, media queries, and styling custom components. However, sharing code between projects can be challenging.

Ultimately all tech choices should come down to the individual project requirements. With this in mind, consider caisy, a high-performing headless CMS built for developers and agency workflows. With caisy, you'll have a flexible and scalable system that successfully utilizes components, documents, and templates. The platform is built to support popular web frameworks such as Next.js, Nuxt, Svelte, and Astro, allowing a seamless and efficient development process.

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. caisy mirrors these principles in its functionality, making it a compelling choice regardless of your chosen CSS styling approach.

So why wait? Create your free account with caisy today! Explore how flexible and adaptable it is to your development approach, be it Styled-Components, CSS Modules, or another styling method. Your ideal CMS tool is just a few clicks away.

Ready For A New Standard?

This was just sneak peek. A tailored no-code editor, reusable components, versioning, starter templates and much more await you: Caisy is the headless CMS you've been dreaming of.

Caisy vs contentful_02