CSS-in-JS Best Practices and Implementation Guide

CSS-in-JS is a popular approach to styling web applications, and for good reason. It allows for a more efficient and scalable way of managing styles, especially in complex applications.

By separating styles from the rest of the code, CSS-in-JS libraries like Emotion and Styled Components help reduce the risk of CSS specificity issues and make it easier to reason about the styles of your application.

One of the key benefits of CSS-in-JS is that it enables you to write styles as JavaScript functions, which can be reused and composed together to create complex styles.

CSS-in-JS libraries have been gaining traction since component-based JavaScript frameworks appeared in front-end development.

A well-designed CSS-in-JS library can solve the problems of managing dependencies and styling single-page applications (SPAs) efficiently.

Components can run independently, without relying on any external CSS file, thanks to CSS-in-JS libraries.

There are many CSS-in-JS libraries, each with unique features and benefits, such as Styled Components, Emotion, Stiches, or Vanilla Extract, JSS, and Aphrodite.

These libraries aim to make JavaScript styling more manageable and maintainable.

CSS-in-JS libraries changed the way we think about and approach styling websites and applications, encouraging component-based design.

They take advantage of JavaScript's features, such as variables, conditional statements, and functions, to create dynamic styles and adapt them to various situations.

This results in a cleaner code and offers new ways to create and manage dynamic styles and designs.

Unfortunately, there is an additional learning curve with CSS-in-JS libraries, as each library might have its own way of writing styles.

Here's a rundown of some popular CSS-in-JS libraries to consider.

Styled-components is one particularly interesting concept that's become more mainstream thanks to Max Stoiber's project.

If you're looking for alternatives, some other notable libraries include those that abstract CSS to the component level itself using JavaScript to describe styles in a declarative and maintainable way.

Each of these libraries comes with slightly different features and syntax, so it's worth doing some research to decide which one is the best fit for your needs.

CSS-in-JS libraries differ in syntax, framework support, and scope handling, but each has unique capabilities not found in others. Some libraries offer global selectors, while others provide state-based styling or client vs. server-side rendering.

A comparison table by Michele Bertoli highlights the most important features of multiple CSS-in-JS libraries. This table can be a valuable resource for developers looking to choose the best library for their project.

CSS-in-JS libraries also offer features like caching, source maps, auto-prefixing, media queries, selector nesting, and built-in support for animations. Some libraries even come with additional plugins and packages, making them a one-stop-shop for styling needs.

CSS-in-JS libraries offer a range of unique features that set them apart from one another.

Global selectors are a feature found in these libraries, allowing for more flexibility in styling.

Some libraries offer state-based styling, which enables dynamic changes to an application's appearance based on its state.

Client vs. server-side rendering is another unique capability, with some libraries supporting both options.

Caching is also a notable feature, helping to improve the performance of applications.

Source maps are included in some libraries, making it easier to debug issues.

Built-in auto-prefixing is a feature that saves developers time and effort.

Media queries are supported by many libraries, allowing for responsive design.

Selector nesting is another feature that's gaining popularity.

Built-in support for animations is also available in some libraries, making it easier to create engaging user experiences.

Additional plugins and packages can be used to further enhance the capabilities of these libraries.

In some CSS-in-JS libraries, template literals are used instead of objects to create styles. This is the case with Styled Components, where styles can be created using template literals.

Template literals are not currently supported by Panda CSS, but the library author is working on adding this capability.

Using template literals can be a more concise way to create styles, but it's worth noting that Panda CSS is still in the process of implementing this feature.

Local scoping is a challenge in CSS, with each style rule having a global scope by default. This can lead to styles overriding each other in surprising ways.

Front-end developers have created methodologies like BEM, OOCSS, and SMACSS to add modularity to CSS, and pre-processors and PostCSS are another way to modularize CSS. CSS-in-JS libraries take this concept to the next level by automating scoping.

Styled Components, a popular CSS-in-JS library, generates a unique class name for each component, allowing for predictable styling. It also supports nesting CSS selectors, as you would do with Sass.

Scoping is a well-known CSS challenge, and CSS-in-JS libraries aim to achieve it without compromising the authoring experience.

Most CSS-in-JS libraries, such as JSS, Emotion, and Styled Components, automatically generate unique selectors for each component to handle scoping. This is evident on Styled Components' homepage, where inspecting an example with a browser's developer tools reveals unique classes generated for each component.

Styled Components generates two unique classes for a button and its parent div, like components__SecondButton-sc-1gmolv7-3 fWxBIM and components__AlignCenter-sc-1gmolv7-0 hjdyfl. This approach creates absolutely unique selectors that prevent CSS specificity problems.

Using inline CSS on the fly, like Radium, leads to more readable HTML code and has advantages such as better performance and source order independence. This approach also enables dead code elimination, which can improve the overall efficiency of a project.

However, inline styles have some shortcomings, as noted in Radium's documentation, which mentions that this approach has its own set of trade-offs.

Scoping is a well-known CSS challenge, and it's the idea of writing styles that don't leak outside of the component, thus avoiding unintended side effects.

By default, CSS doesn't allow local scoping, so each style rule has a global scope, applying to the entire project, which can lead to styles overriding each other in surprising ways.

Front-end developers have created methodologies like BEM, OOCSS, and SMACSS to add modularity to CSS, and pre-processors and PostCSS are another way to modularize CSS.

Pre-processors and PostCSS help automate scoping, leading to a high level of predictability.

CSS-in-JS libraries take this concept to the next level by automating scoping, making it easier to write styles that don't leak outside of the component.

One popular CSS-in-JS library is Styled Components, which is used by notable companies like BBC, Reddit, Vimeo, and Lego.

Conditional styles allow us to apply sets of styles conditionally, but they can be limiting when we want to have a variety of styles.

For instance, if we want to have specific buttons for different platforms like Twitter, Facebook, and Pinterest, we can't simply switch between predefined styles.

Conditional styles can only apply sets of styles conditionally, such as applying the class "primary" and defining its styles in a separate CSS file.

This approach becomes unmanageable when we want to have a variety of styles.

Inline styles might seem like a solution, but they don't support pseudo-classes, attribute selectors, media queries, or the like.

Styled JSX is a CSS-in-JS library that adds full CSS support for the JSX syntax. It's a great tool for adding styles to your React components.

The runtime size of Styled JSX is just 3 kBytes when it's gzipped and minified. This makes it a lightweight option for adding styles to your components.

Styled JSX supports all CSS features, including vendor prefixing, source maps, and dynamic style support. This means you can use all the standard CSS features you're used to, but with the added benefit of being able to use JSX syntax.

One of the benefits of Styled JSX is that it can be used both on the client and server side. This makes it a great option for server-side rendering or isomorphic rendering.

Here are some key features of Styled JSX:

The code example below shows how to use Styled JSX to change the color of a paragraph to red:

```css

.jsx-123 {

color: red;

}

```

This code uses the ES6 template literal notation to add a CSS style to a JSX component. The resulting CSS will be injected into the DOM, allowing you to style your components with ease.

Pseudo Elements are a powerful tool in Panda CSS, allowing you to target specific states of an element, such as hover, active, and focus.

With Panda CSS, you can change text and background colors on hover by adding the _hover property. This property will override the default value specified in the base property.

You can also target the first, last, odd, and even children of an element by adding the _first, _last, _odd, and _even prefixes to the style property.

For example, you can use the _hover property to change the text color and background color of an element when a user hovers over it.

In CSS-in-JS, the design and development considerations are crucial to a project's success.

One advantage of CSS-in-JS libraries is that they eliminate the need for global CSS variables, which can make code harder to manage.

As mentioned, CSS-in-JS libraries also offer advantages such as improved code organization and reusability.

However, implementing CSS-in-JS can be challenging, especially for developers without prior experience with JavaScript or CSS-in-JS libraries.

Despite this, CSS-in-JS libraries can greatly simplify the development process by allowing developers to write CSS code directly in their JavaScript files.

Using a CSS-in-JS library offers several advantages, including the ability to apply complex logic to style rules, such as loops, conditionals, variables, state-based styling, and more.

This allows for dynamic functionality in your UI, making it an ideal solution for complicated designs that require real-time updates.

With CSS-in-JS, you can create a more responsive and interactive user experience, which is especially beneficial for applications that need to adapt to changing user input or data.

By leveraging the power of JavaScript, CSS-in-JS libraries enable you to write more efficient and maintainable code, which can lead to faster development times and reduced debugging efforts.

CSS-in-JS has a steep learning curve, especially for those unfamiliar with component-based frameworks or web components. This is because it requires learning new syntax and a new way of thinking.

The syntax itself can be a barrier to entry, taking time to become comfortable with. This can slow down your development workflow for a while.

Picking up a new way of thinking is also crucial when adopting CSS-in-JS. This means adapting to a different mindset and approach to coding.

Tokens are a convenient way to use standardized values in your design, and Panda CSS offers a number of built-in tokens for colors, sizes, spacings, and more.

These tokens can be configured in the panda.config.ts file, where you can specify values like blue.100 for the background and blue.800 for the text color.

The 3xl token is used for the font size, which is a great example of how tokens can simplify your design work.

If you want to see all the core tokens available by default, you can look into the styled-system/tokens/tokens.d.ts file.

Instead of writing out long CSS properties like background-color, border-radius, and padding, you can use shorter tokens like bg, rounded, and p.