Build-variants

Declaratively build style objects based on your React component props with a clean, type-safe API.

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Introduction

Build-variants helps you organize and compose CSS (or any style values) based on component props. It separates styling logic from component logic, making your code easier to maintain and extend. Note that it is a builder—it doesn’t apply styles by itself but returns an object your CSS-in-JS library can use.

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Installation

npm install @productive-codebases/build-variants

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Usage

1. Setup Your Factory Function

Configure build-variants with your styling engine. For example, with styled-components:

import type { CSSObject } from '@emotion/react'
import { newBuildVariants } from '@productive-codebases/build-variants'

export function buildVariants<TProps extends object>(props: TProps) {
  return newBuildVariants<TProps, CSSObject>(props)
}

This sets up a function that accepts props and returns a builder configured for CSSObject objects.

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2. Decorate a Component

Integrate the builder with any styled function that accepts a CSSObject-like object. Whether you're using Emotion, styled-components, MUI, or any other library, the generated style object will work seamlessly.

import styled from '@emotion/styled'
// Alternatively:
// import styled from 'styled-components'
// or import { styled } from '@mui/material', etc.
import { buildVariants } from './buildVariants'

const Div = styled.div(props => buildVariants(props).end())

export default function Button() {
  return <Div>My Button</Div>
}

In this example, no extra styles are added; the builder returns an empty style object.

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3. Adding CSS Blocks

Chain CSS blocks to add styles:

const Div = styled.div(props => {
  return buildVariants(props)
    .css({
      display: 'inline-block',
      padding: '10px'
    })
    .css({
      background: 'blue',
      color: 'white'
    })
    .end()
})

Applied styles:

• display: inline-block
• padding: 10px
• background: blue
• color: white

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4. Declaring Variants

Simple Variant

Define a style variant based on a prop value:

import styled from '@emotion/styled'
import { buildVariants } from './buildVariants'

interface IButtonProps {
  type: 'primary' | 'secondary'
}

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    .css({
      display: 'inline-block',
      padding: '10px'
    })
    .variant('type', props.type, {
      primary: {
        background: 'blue',
        color: 'white'
      },
      secondary: {
        background: 'silver',
        color: 'black'
      }
    })
    .end()
})

export default function Button(props: IButtonProps) {
  return <Div type={props.type}>My Button</Div>
}

Applied styles:

• When type="primary":

  • Common: display: inline-block, padding: 10px
  • Variant: background: blue, color: white

• When type="secondary":

  • Common: display: inline-block, padding: 10px
  • Variant: background: silver, color: black

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Multiple Variants

Allow multiple variant values (e.g., text styles):

interface IButtonProps {
  type: 'primary' | 'secondary'
  text?: Array<'strong' | 'success' | 'error'>
}

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    .css({
      display: 'inline-block',
      padding: '10px'
    })
    .variant('type', props.type, {
      primary: {
        background: 'blue',
        color: 'white'
      },
      secondary: {
        background: 'silver',
        color: 'black'
      }
    })
    .variants('text', props.text, {
      strong: { fontWeight: 'bold' },
      success: { color: 'green' },
      error: { color: 'red' }
    })
    .end()
})

Usage example:

// Renders a primary button with both bold and red text styles
<Button type="primary" text={['strong', 'error']} />

Applied styles:

• Type "primary": background: blue, color: white
• Text variants:
  • strong adds fontWeight: bold
  • error adds color: red Note: In case of conflicting styles (like two colors), the later applied style wins.

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Compound Variants

Compose multiple variants using private (internal) and public (external) props:

interface IButtonProps {
  // Private variants (used for composing public ones)
  _background?: 'primary' | 'secondary' | 'success' | 'error'
  _text?: Array<'dark' | 'light' | 'success' | 'error' | 'strong'>
  // Public variant: the component's API
  type: 'primary' | 'secondary' | 'success' | 'error'
  children: string
}

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    .css({
      display: 'inline-block',
      padding: '10px'
    })
    // Define private variants first.
    .variant('_background', props._background, {
      primary: { background: 'blue' },
      secondary: { background: 'silver' },
      success: { background: '#eaff96' },
      error: { background: '#ffdbdb' }
    })
    .variants('_text', props._text, {
      dark: { color: 'black' },
      light: { color: 'white' },
      success: { color: 'green' },
      error: { color: 'red' },
      strong: { fontWeight: 'bold' }
    })
    // Define compound variants mapping public 'type' to private ones.
    .compoundVariant('type', props.type, {
      primary: builder_ =>
        builder_.get('_background', 'primary').get('_text', ['light']).end(),
      secondary: builder_ =>
        builder_.get('_background', 'secondary').get('_text', ['dark']).end(),
      success: builder_ =>
        builder_.get('_background', 'success').get('_text', ['success']).end(),
      error: builder_ =>
        builder_
          .get('_background', 'error')
          .get('_text', ['error', 'strong'])
          .css({ border: '1px solid red' })
          .end()
    })
    .end()
})

Usage examples:

<Button type="primary">Primary button</Button>
<Button type="secondary">Secondary button</Button>
<Button type="success">Success button</Button>
<Button type="error">Error button</Button>

Applied styles:

• Primary:

  • Private _background: primary → background: blue
  • Private _text: ['light'] → color: white

• Secondary:

  • Private _background: secondary → background: silver
  • Private _text: ['dark'] → color: black

• Success:

  • Private _background: success → background: #eaff96
  • Private _text: ['success'] → color: green

• Error:

  • Private _background: error → background: #ffdbdb
  • Private _text: ['error', 'strong'] → color: red and fontWeight: bold
  • Additional style: border: 1px solid red

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5. Overriding with Private Variants

Private variants have a higher precedence than public ones, allowing you to override the default behavior for specific use cases.

<Button type="error">Error button</Button>

<Button type="error" _background="success">
  Error button with success background
</Button>

Applied styles:

• The first button applies the default compound variant for error.
• The second button overrides the _background variant to "success", so it receives background: #eaff96 (as defined in the success mapping) while keeping the other error-related styles.

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6. Conditional Blocks

Enable or skip blocks of styles based on a condition:

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    // Other style blocks…
    .if(props.applyTextVariant === true, builder_ => {
      return builder_
        .variants('_text', props._text, {
          dark: { color: 'black' },
          light: { color: 'white' },
          success: { color: 'green' },
          error: { color: 'red' },
          strong: { fontWeight: 'bold' }
        })
        .end()
    })

    // Alternatively, if you only need to add simple CSS:
    // .if(props.applyTextVariant === true, {
    //   color: 'red'
    // })

    .compoundVariant('type', props.type, {
      // …
    })
    .end()
})

Applied styles:

• If applyTextVariant is true, the text-related styles are applied. Otherwise, they are skipped.

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7. Blocks Weight

Control the order of style application by assigning a weight to each block:

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    .css({
      display: 'inline-block',
      padding: '10px'
    })
    .css(
      { color: 'silver' },
      { weight: 10 }  // This block is applied later.
    )
    .variants('_text', props._text, {
      dark: { color: 'black' },
      // …
    })
    .end()
})

Applied styles:

• The color: silver style with weight 10 overrides any earlier conflicting color from _text if applied later.

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8. Debugging

Log internal builder state to help diagnose complex style applications:

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    // Other style definitions…
    .debug()
    .end()
})

Or enable debugging conditionally:

interface IButtonProps {
  debug?: boolean
}

const Div = styled.div<IButtonProps>(props => {
  return buildVariants(props)
    // Other style definitions…
    .debug(props.debug === true)
    .end()
})

Result: Detailed logs in the console show which styles are applied and the builder's internal state.

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Examples

• https://codesandbox.io/s/1-init-b5t24e?file=/src/buildVariants.ts
• https://codesandbox.io/s/1-init-b5t24e?file=/src/Button.tsx
• https://codesandbox.io/s/2-add-css-0zmimn?file=/src/Button.tsx
• https://codesandbox.io/s/3-add-variant-9b3bvh?file=/src/Button.tsx
• https://codesandbox.io/s/4-multiple-variants-v9bxds?file=/src/Button.tsx
• https://codesandbox.io/s/5-variants-composition-m6b5zs?file=/src/Button.tsx
• https://codesandbox.io/s/overrides-with-private-variants-w72ed1?file=/src/App.tsx
• https://codesandbox.io/s/7-condition-blocks-0xko7x?file=/src/Button.tsx
• https://codesandbox.io/s/8-blocks-weight-d0fbz3?file=/src/Button.tsx
• https://codesandbox.io/s/9-debug-f6ozbu?file=/src/Button.tsx:463-2386

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Summary

Build-variants empowers you to:

• Declare and compose style variants with a clean, declarative, and type-safe API.
• Separate styling logic from component code.
• Support multiple, compound, and conditional variants for flexible component design.
• Control style precedence with block weights.
• Debug style composition effortlessly.

Enjoy building maintainable, flexible UI components with Build-variants!