1aron/cva

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 (WorkOS)
  Huge thanks to the WorkOS team for pioneering the variants API movement – your open-source contributions are immensely appreciated
• clb (Bill Criswell)
  This project originally started out with the intention of merging into the wonderful clb 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

1. Alias the package with npm install

   npm i cva@npm:class-variance-authority

2. 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.

Tru Narla did a wonderful overview of cva at Next.js Conf 2022 – you should check it out before continuing:

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

VariantProps

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(/* … */);

Required Variants

To keep the API small and unopionated, cva doesn't offer a built-in solution for setting required variants.

Instead, we recommend using TypeScript's Utility Types:

// components/button.ts
import { cva, type VariantProps } from "class-variance-authority";

export type ButtonVariantProps = VariantProps<typeof button>;
export const buttonVariants = cva("…", {
  variants: {
    optional: { a: "…", b: "…" },
    required: { a: "…", b: "…" },
  },
});

/**
 * Button
 */
export interface ButtonProps
  extends Omit<ButtonVariantProps, "required">,
    Required<Pick<ButtonVariantProps, "required">> {}

export const button = (props: ButtonProps) => buttonVariants(props);

// ❌ TypeScript Error:
// Argument of type "{}": is not assignable to parameter of type "ButtonProps".
//   Property "required" is missing in type "{}" but required in type
//   "ButtonProps".
button({});

// ✅
button({ required: "a" });

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

1. base: the base class name (string, string[] or null)
2. 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 as null

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>

How Can I Create Responsive Variants like Stitches.js?

You can't.

cva doesn't know about how you choose to apply CSS clases, and it doesn't want to.

We recommend either:

• Showing/hiding elements with different variants, based on your preferred breakpoint.

  Example: With Tailwind

  export const Example = () => (
    <>
      <div className="hidden sm:inline-flex">
        <button className={button({ intent: "primary" })}>
          Hidden until sm
        </button>
      </div>
      <div className="inline-flex sm:hidden">
        <button className={button({ intent: "secondary" })}>
          Hidden after sm
        </button>
      </div>
    </>
  );

• Create a bespoke variant that changes based on the breakpoint.

  e.g. button({ intent: "primaryUntilMd" })

Note

This is something I've been thinking about since the project's inception, and I've gone back and forth many times on the idea of building it. It's a large undertaking and brings all the complexity of supporting many different build tools and frameworks.

In my experience, "responsive variants" are typically rare, and hiding/showing different elements is usually good enough to get by.

To be frank, I'm probably not going to build/maintain a solution unless someone periodically gives me a thick wad of cash to do so, and even then I'd probably rather spend my free time living my life.