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Class Variance Authority
cva
Class Variance Authority
Introduction
CSS-in-TS libraries such as Stitches and Vanilla Extract are fantastic options for building type-safe UI components; taking away all the worries of class names and StyleSheet composition.
…but CSS-in-TS (or CSS-in-JS) isn't for everyone.
You may need full control over your StyleSheet output. Your job might require you to use a framework such as Tailwind CSS. You might just prefer writing your own CSS.
Creating variants with the "traditional" CSS approach can become an arduous task; manually matching classes to props and manually adding types.
cva
aims to take those pain points away, allowing you to focus on the more fun aspects of UI development.
Acknowledgements
-
Stitches (Modulz)
Huge thanks to the Modulz team for pioneering thevariants
API movement – your open-source contributions are immensely appreciated -
clb (Bill Criswell)
This project originally started out with the intention of merging into the wonderfulclb
library, but after some discussion with Bill, we felt it was best to go down the route of a separate project.
I'm so grateful to Bill for sharing his work publicly and for getting me excited about building a type-safe variants API for classes. If you have a moment, please go and star the project on GitHub. Thank you Bill! - Vanilla Extract (Seek)
Installation
npm i class-variance-authority
"Do I really have to write such a long package name for every import?"
Unfortunately, yes. Originally, the plan was the publish the package as cva
, but this name has been taken and marked as a "placeholder". I've reached out to the author and NPM support, but have yet to hear back.
In the meantime, you can always alias the package for your convenience…
Aliasing
-
Alias the package with
npm install
npm i cva@npm:class-variance-authority
-
Then import like so:
import { cva } from "cva"; // …
Tailwind CSS IntelliSense
If you're using the "Tailwind CSS IntelliSense" Visual Studio Code extension, you can enable autocompletion inside cva
by adding the following to your settings.json
:
{
"tailwindCSS.experimental.classRegex": [
["cva\\(([^)]*)\\)", "[\"'`]([^\"'`]*).*?[\"'`]"]
]
}
Getting Started
Disclaimer: Although
cva
is a tiny library, it's best to use in a SSR/SSG environment – your user probably doesn't need this JavaScript, especially for static components.
Your First Component
To kick things off, let's build a "basic" button
component, using cva
to handle our variant's classes
Note: Use of Tailwind CSS is optional
// components/button.ts
import { cva } from "class-variance-authority";
const button = cva(["font-semibold", "border", "rounded"], {
variants: {
intent: {
primary: [
"bg-blue-500",
"text-white",
"border-transparent",
"hover:bg-blue-600",
],
// **or**
// primary: "bg-blue-500 text-white border-transparent hover:bg-blue-600",
secondary: [
"bg-white",
"text-gray-800",
"border-gray-400",
"hover:bg-gray-100",
],
},
size: {
small: ["text-sm", "py-1", "px-2"],
medium: ["text-base", "py-2", "px-4"],
},
},
compoundVariants: [{ intent: "primary", size: "medium", class: "uppercase" }],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
button();
// => "font-semibold border rounded bg-blue-500 text-white border-transparent hover:bg-blue-600 text-base py-2 px-4 uppercase"
button({ intent: "secondary", size: "small" });
// => "font-semibold border rounded bg-white text-gray-800 border-gray-400 hover:bg-gray-100 text-sm py-1 px-2"
Additional Classes
All cva
components provide an optional class
prop, which can be used to pass additional classes to the component.
// components/button.ts
import { cva } from "class-variance-authority";
const button = cva(/* … */);
button({ class: "m-4" });
// => "…buttonClasses m-4"
TypeScript Helpers
cva
offers the VariantProps
helper to extract variant types
// components/button.ts
import type { VariantProps } from "class-variance-authority";
import { cva, cx } from "class-variance-authority";
/**
* Button
*/
export type ButtonProps = VariantProps<typeof button>;
export const button = cva(/* … */);
Composing Components
Whilst cva
doesn't yet offer a built-in method for composing components, it does offer the tools to extend components on your own terms…
For example; two cva
components, concatenated together with cx
:
// components/card.ts
import type { VariantProps } from "class-variance-authority";
import { cva, cx } from "class-variance-authority";
/**
* Box
*/
export type BoxProps = VariantProps<typeof box>;
export const box = cva(["box", "box-border"], {
variants: {
margin: { 0: "m-0", 2: "m-2", 4: "m-4", 8: "m-8" },
padding: { 0: "p-0", 2: "p-2", 4: "p-4", 8: "p-8" },
},
defaultVariants: {
margin: 0,
padding: 0,
},
});
/**
* Card
*/
type CardBaseProps = VariantProps<typeof cardBase>;
const cardBase = cva(["card", "border-solid", "border-slate-300", "rounded"], {
variants: {
shadow: {
md: "drop-shadow-md",
lg: "drop-shadow-lg",
xl: "drop-shadow-xl",
},
},
});
export interface CardProps extends BoxProps, CardBaseProps {}
export const card = ({ margin, padding, shadow }: CardProps = {}) =>
cx(box({ margin, padding }), cardBase({ shadow }));
API Reference
cva
Builds a cva
component
const component = cva("base", options);
Parameters
-
base
: the base class name (string
,string[]
ornull
) -
options
(optional)-
variants
: your variants schema -
compoundVariants
: variants based on a combination of previously defined variants -
defaultVariants
: set default values for previously defined variants.
note: these default values can be removed completely by setting the variant asnull
-
Returns
A cva
component function
cx
Concatenates class names
const className = cx(classes);
Parameters
-
classes
: array of classes to be concatenated
Returns
string
Examples
⚠️ Warning: The examples below are purely demonstrative and haven't been tested thoroughly (yet)
Astro
---
import { cva, type VariantProps } from "class-variance-authority";
const button = cva("button", {
variants: {
intent: {
primary: [
"bg-blue-500",
"text-white",
"border-transparent",
"hover:bg-blue-600",
],
secondary: [
"bg-white",
"text-gray-800",
"border-gray-400",
"hover:bg-gray-100",
],
},
size: {
small: ["text-sm", "py-1", "px-2"],
medium: ["text-base", "py-2", "px-4"],
},
},
compoundVariants: [{ intent: "primary", size: "medium", class: "uppercase" }],
});
interface Props extends VariantProps<typeof button> {}
/**
* For Astro components, we recommend setting your defaultVariants within
* Astro.props (which are `undefined` by default)
*/
const { intent = "primary", size = "medium" } = Astro.props;
---
<button class={button({ intent, size })}>
<slot />
</button>
BEM
/* styles.css */
.button {
/* */
}
.button--primary {
/* */
}
.button--secondary {
/* */
}
.button--small {
/* */
}
.button--medium {
/* */
}
.button--primary-small {
/* */
}
import { cva } from "class-variance-authority";
const button = cva("button", {
variants: {
intent: {
primary: "button--primary",
secondary: "button--secondary",
},
size: {
small: "button--small",
medium: "button--medium",
},
},
compoundVariants: [
{ intent: "primary", size: "medium", class: "button--primary-small" },
],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
button();
// => "button button--primary button--medium"
button({ intent: "secondary", size: "small" });
// => "button button--secondary button--small"
11ty (with Tailwind)
// button.11ty.js
const { cva } = require("class-variance-authority");
// ⚠️ Disclaimer: Use of Tailwind CSS is optional
const button = cva("button", {
variants: {
intent: {
primary: [
"bg-blue-500",
"text-white",
"border-transparent",
"hover:bg-blue-600",
],
secondary: [
"bg-white",
"text-gray-800",
"border-gray-400",
"hover:bg-gray-100",
],
},
size: {
small: ["text-sm", "py-1", "px-2"],
medium: ["text-base", "py-2", "px-4"],
},
},
compoundVariants: [{ intent: "primary", size: "medium", class: "uppercase" }],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
module.exports = function ({ label, intent, size }) {
return `<button class="${button({ intent, size })}">${label}</button>`;
};
React (with CSS Modules)
/* button.module.css */
.base {
/* */
}
.primary {
/* */
}
.secondary {
/* */
}
.small {
/* */
}
.medium {
/* */
}
.primaryMedium {
/* */
}
// button.tsx
import React from "react";
import { cva, type VariantProps } from "class-variance-authority";
import {
base,
primary,
secondary,
small,
medium,
primaryMedium,
} from "./button.module.css";
const button = cva(base, {
variants: {
intent: {
primary,
secondary,
},
size: {
small,
medium,
},
},
compoundVariants: [
{ intent: "primary", size: "medium", class: primaryMedium },
],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
export interface ButtonProps
extends React.HTMLAttributes<HTMLButtonElement>,
VariantProps<typeof button> {}
export const Button: React.FC<ButtonProps> = ({
className,
intent,
size,
...props
}) => (
<button className={button({ intent, size, class: className })} {...props} />
);
React (with Tailwind)
// button.tsx
import React from "react";
import { cva, type VariantProps } from "class-variance-authority";
// ⚠️ Disclaimer: Use of Tailwind CSS is optional
const button = cva("button", {
variants: {
intent: {
primary: [
"bg-blue-500",
"text-white",
"border-transparent",
"hover:bg-blue-600",
],
secondary: [
"bg-white",
"text-gray-800",
"border-gray-400",
"hover:bg-gray-100",
],
},
size: {
small: ["text-sm", "py-1", "px-2"],
medium: ["text-base", "py-2", "px-4"],
},
},
compoundVariants: [{ intent: "primary", size: "medium", class: "uppercase" }],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
export interface ButtonProps
extends React.HTMLAttributes<HTMLButtonElement>,
VariantProps<typeof button> {}
export const Button: React.FC<ButtonProps> = ({
className,
intent,
size,
...props
}) => (
<button className={button({ intent, size, class: className })} {...props} />
);
Svelte
<!-- button.svelte -->
<script lang="ts">
import { cva, type VariantProps } from "class-variance-authority";
const button = cva("button", {
variants: {
intent: {
primary: "button--primary",
secondary: "button--secondary",
},
size: {
small: "button--small",
medium: "button--medium",
},
},
compoundVariants: [
{ intent: "primary", size: "medium", class: "button--primary-medium" },
],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
type ButtonProps = VariantProps<typeof button>;
export let intent: ButtonProps["intent"];
export let size: ButtonProps["size"];
</script>
<button class={button({ intent, size })}><slot /></button>
<style>
.button { /* … */ }
.button--primary { /* … */ }
.button--secondary { /* … */ }
.button--small { /* … */ }
.button--medium { /* … */ }
.button--primary-medium { /* … */ }
</style>
Vue 3
<!-- button.vue -->
<script setup lang="ts">
import { cva, type VariantProps } from "class-variance-authority";
const button = cva("button", {
variants: {
intent: {
primary: "button--primary",
secondary: "button--secondary",
},
size: {
small: "button--small",
medium: "button--medium",
},
},
compoundVariants: [
{ intent: "primary", size: "medium", class: "button--primary-medium" },
],
defaultVariants: {
intent: "primary",
size: "medium",
},
});
type ButtonProps = VariantProps<typeof button>;
defineProps<{
intent: ButtonProps["intent"];
size: ButtonProps["size"];
}>();
</script>
<template>
<button :class="button({ intent, size })">
<slot />
</button>
</template>
<style>
.button {
/* … */
}
.button--primary {
/* … */
}
.button--secondary {
/* … */
}
.button--small {
/* … */
}
.button--medium {
/* … */
}
.button--primary-medium {
/* … */
}
</style>
Other Use Cases
Although primarily designed for handling class names, at its core, cva
is really just a fancy way of managing a string…
Dynamic Text Content
const greeter = cva("Good morning!", {
variants: {
isLoggedIn: {
true: "Here's a secret only logged in users can see",
false: "Log in to find out more…",
},
},
defaultVariants: {
isLoggedIn: "false",
},
});
greeter();
// => "Good morning! Log in to find out more…"
greeter({ isLoggedIn: "true" });
// => "Good morning! Here's a secret only logged in users can see"
FAQs
Why Don't You Provide a styled
API?
Long story short: it's unnecessary.
cva
encourages you to think of components as traditional CSS classes:
- Less JavaScript is better
- They're framework agnostic; truly reusable
- Polymorphism is free; just apply the class to your preferred HTML element
- Less opinionated; you're free to build components with
cva
however you'd like
Example: Polymorphic Components
There's no as
prop in cva
, because HTML is free:
-- // A familiar `styled` button as a link
-- <Button as="a" href="#" variant="primary">Button as a link</Button>
++ // A `cva` button as a link
++ <a href="#" class={button({variant: "primary"})}>Button as a link</a>