cva

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 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!

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 in TypeScript

Add the alias to your tsconfig.json paths:

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "cva": ["node_modules/class-variance-authority"]
    }
  }
}

Then import like so:
```
import { cva } from "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

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"

TypeScript Helpers

cva offers the VariantProps helper to extract variant types

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

/**
 * YourComponent
 */
export type YourComponentProps = VariantProps<typeof yourComponent>;
export const yourComponent = cva(/* ... */);

Composing Classes

Whilst cva doesn't yet offer a built-in method for composing classes, it does offer the tools to extend components on your own terms…

For example; two cva styles, concatenated together with cx:

// styles/components.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 class variance authority

const component = cva("base", options);

base: the base class name (string, string[] or null)
options (optional)
- variants: your variants schema
- compoundVariants: variants based on a combination of previously defined variants
- defaultVariants: set default values for previously defined variants

`cx`

Concatenates class names

const className = cx(classes);

classes: array of classes to be concatenated

Examples

⚠️ Warning: The examples below are purely demonstrative and haven't been tested thoroughly (yet)

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.css */
.base {
  /* */
}

.primary {
  /* */
}
.secondary {
  /* */
}

.small {
  /* */
}
.medium {
  /* */
}

.primaryMedium {
  /* */
}

// button.tsx
import React from "react";
import { cva } from "class-variance-authority";
import type { VariantProps } from "class-variance-authority";

import {
  base,
  primary,
  secondary,
  small,
  medium,
  primaryMedium,
} from "./button.css";

// ⚠️ Disclaimer: Use of Tailwind CSS is optional
const button = cva(base, {
  variants: {
    intent: {
      primary,
      secondary,
    },
    size: {
      small,
      medium,
    },
  },
  compoundVariants: [
    { intent: "primary", size: "medium", class: primaryMedium },
  ],
  defaultVariants: {
    intent: "primary",
    size: "medium",
  },
});

export type ButtonProps = VariantProps<typeof button>;

export const Button: React.FC<ButtonProps> = ({ intent, size, ...props }) => (
  <button className={button({ intent, size })} {...props} />
);

React (with Tailwind)

// button.tsx
import React from "react";
import { cva } from "class-variance-authority";
import 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 type ButtonProps = VariantProps<typeof button>;

export const Button: React.FC<ButtonProps> = ({ intent, size, ...props }) => (
  <button className={button({ intent, size })} {...props} />
);

Svelte

<!-- button.svelte -->
<script lang="ts">
  import { cva } from "class-variance-authority";
  import 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>

<!-- button.vue -->
<script lang="ts">
import { defineComponent } from "vue";

import { cva } from "class-variance-authority";
import 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 default defineComponent({
  props: ["intent" as ButtonProps["intent"], "size" as ButtonProps["size"]],
  methods: {
    button,
  },
});
</script>

<template>
  <button :class="button({ intent, size })">
    <slot></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"

essejmclean / cva

cva