Styling in React: CSS-in-JS vs. CSS Modules

Welcome to our React.js series, where we explore key concepts and tools that will take you from a beginner to an expert in React development. In this blog, we’ll dive into the realm of styling in React applications. Specifically, we’ll compare two popular approaches: CSS-in-JS and CSS Modules. Choosing the right styling method is essential for maintaining clean, maintainable, and efficient code. Let’s explore these two approaches and understand when to use each one.

The Importance of Styling in Web Development

Styling plays a crucial role in web development. It not only enhances the visual appeal of your web application but also contributes to user experience. As a React developer, you have various options for applying styles to your components. In this blog, we’ll focus on two widely used methods: CSS-in-JS and CSS Modules.

CSS-in-JS: A Dynamic Approach

CSS-in-JS is an innovative approach that allows you to write and manage CSS styles directly within your JavaScript code. It’s particularly beneficial for building component-based applications, as it encourages the creation of scoped styles specific to each component.

Key Features of CSS-in-JS:

  • Dynamic Styles: CSS-in-JS enables dynamic styling based on component props and states, making it suitable for responsive design.
  • Scoped Styles: Each component can have its isolated styles, reducing the risk of CSS conflicts.
  • JavaScript Integration: It seamlessly integrates with your JavaScript code, allowing you to use variables, functions, and logic to define styles.
  • Popular Libraries: There are popular libraries like Styled-components and Emotion that implement CSS-in-JS in React applications.

CSS Modules: A Modular Approach

CSS Modules offer a different approach to styling. They provide a way to encapsulate styles at the component level by generating unique class names for each module. This approach promotes modularity and reusability of styles.

Key Features of CSS Modules:

  • Isolation: CSS Modules create local scope for styles, reducing the chance of global CSS conflicts.
  • Explicit Imports: You can import CSS modules explicitly in your JavaScript files, allowing you to use styles as objects.
  • Familiar Syntax: CSS Modules use standard CSS syntax, making it familiar to most developers.
  • Build Process: CSS Modules require a build step to generate unique class names.

Pros and Cons of CSS-in-JS


  1. Scoped Styles: Styles are scoped to individual components, reducing the risk of naming collisions.
  2. Dynamic Styling: Reactivity is easily achieved by using JavaScript variables and conditions.
  3. Ease of Maintenance: CSS-in-JS keeps styles close to the component, making it easier to maintain and refactor.


  1. Performance Overhead: Some CSS-in-JS solutions may introduce a performance overhead due to runtime style generation.
  2. Learning Curve: Developers familiar with traditional CSS may need time to adapt to the JavaScript-centric approach.

Pros and Cons of CSS Modules


  1. Isolation: CSS Modules provide local scope for styles, ensuring encapsulation.
  2. Explicit Imports: Styles are explicitly imported into components, making it clear which styles are used where.
  3. Familiar Syntax: Developers with CSS experience will find CSS Modules easy to grasp.


  1. Build Step: CSS Modules require a build step to generate unique class names, which might complicate the development setup.
  2. Less Dynamic: Achieving dynamic styles may require more effort compared to CSS-in-JS solutions.

Choosing the Right Approach

Choosing between CSS-in-JS and CSS Modules depends on your project’s specific requirements and your team’s preferences. Consider the following factors:

  • Project Size: For smaller projects, CSS Modules might suffice. For larger projects with complex styling needs, CSS-in-JS may be more suitable.
  • Team Familiarity: Consider your team’s expertise and familiarity with the chosen approach.
  • Performance: Evaluate whether the performance overhead of CSS-in-JS is acceptable for your application.

Real-World Example: Styling a Component

Let’s illustrate the differences between CSS-in-JS and CSS Modules with a practical example. We’ll create a simple button component and style it using both approaches.

jsxCopy code// CSS-in-JS using Styled-components

import styled from 'styled-components';

const StyledButton = styled.button`
  background-color: ${(props) => (props.primary ? 'blue' : 'gray')};
  color: white;
  padding: 10px 20px;
  border: none;
  cursor: pointer;

// CSS Modules

import styles from './Button.module.css';

function Button(props) {
  const buttonClass = props.primary ? styles.primary : styles.secondary;

  return (
    <button className={`${styles.button} ${buttonClass}`} onClick={props.onClick}>

In this example, the StyledButton component uses CSS-in-JS with Styled-components, while the Button component uses CSS Modules. Each component applies styles based on the primary prop.


Styling in React is a critical aspect of web development, and choosing the right approach is essential for maintaining clean and maintainable code. CSS-in-JS and CSS Modules are both powerful tools, each with its unique strengths and considerations. As you continue your journey from beginner to expert in React.js, you’ll gain a deeper understanding of when and how to use each styling method effectively.

For further insights and tutorials on React development, consider visiting

Remember that the choice between CSS-in-JS and CSS Modules is not about which is better overall, but rather about which is better suited to your project’s specific needs and your team’s preferences. Happy styling and coding!


  1. Styled-components Documentation:
  2. Emotion Documentation:
  3. CSS Modules Documentation:

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