macro-components

Create flexible layout and composite UI components without the need to define arbitrary custom props.

npm i macro-components

import React from 'react'
import styled from 'styled-components'
import Macro from 'macro-components'
import { space, fontSize, color } from 'styled-system'
 
// Define some styled-components
const Box = styled.div`${space} ${fontSize} ${color}`
Box.displayName = 'Box'
 
const Image = styled.img`
  max-width: 100%;
  height: auto;
  ${space}
`
Image.displayName = 'Image'
 
const Heading = styled.h2`${space} ${fontSize} ${color}`
Heading.displayName = 'Heading'
 
const Text = styled.div`${space} ${fontSize} ${color}`
Text.displayName = 'Text'
 
// create a macro function with the UI components you intend to use
const macro = Macro({
  Image,
  Heading,
  Text
})
 
// Create a macro-component
const MediaObject = macro(({
  Image,
  Heading,
  Text
}) => (
  <Flex p={2} align='center'>
    <Box width={128}>
      {Image}
    </Box>
    <Box>
      {Heading}
      {Text}
    </Box>
  </Flex>
))

import MediaObject from './MediaObject'
 
// get the macro component's child components
const { Image, Heading, Text } = MediaObject
 
// Use the macro-component by passing the components as children
const App = props => (
  <div>
    <MediaObject>
      <Image src='kitten.png' />
      <Heading>
        Hello
      </Heading>
      <Text>
        This component keeps its tree structure but still allows for regular composition.
      </Text>
    </MediaObject>
  </div>
)

Features

• Single component creator
• Intended for use with libraries like styled-components & glamorous
• Encapsulate layout structure in composable components
• Help keep your component API surface area to a minimum
• Works with any other React components

Note: Macro components are intended to only work with specific child components. If you're wanting to define slots, see the Alternatives section below.

Motivation

Often it's best to use React composition and props.children to create UI that is composed of multiple elements, but sometimes you might want to create larger composite components with encapsulated tree structures for layout or create Bootstrap-like UI components such as panels, cards, or alerts. This library lets you create composite components with encapsulated DOM structures without the need to define arbitrary props APIs and that work just like any other React composition.

This can help ensure that your component API surface area remains small and easier to maintain.

If you find yourself creating composite React components that don't map to data structures, as described in Thinking in React, then this module is intended for you.

Usage

Macro(componentsObject)(elementFunction)

Returns a React component with a composable API that keeps tree layout structure.

const Banner = Macro({
  // pass a components object
  Heading,
  Subhead
})(({
  // the element function receives child elements
  // named according to the components object
  Heading,
  Subhead
}) => (
  <Box p={3} color='white' bg='blue'>
    {Heading}
    {Subhead}
  </Box>
)

The elementFunction argument is called with an object of elements based on the componentsObject passed to the Macro function. Using the Banner component above would look something like the following.

import Banner from './Banner'
 
const App = () => (
  <Banner>
    <Banner.Heading>Hello</Banner.Heading>
    <Banner.Subhead>Subhead</Banner.Subhead>
  </Banner>
)

componentsObject

The components object is used to defined which components the macro component will accept as children.

elementFunction

The element function is similar to a React component, but receives an elements object as its first argument and props as its second one. The elements object is created from its children and is intended to make encapsulating composition and element structures easier.

Within the macro component, the element function is called with the elements object and props: elementFunction(elementsObject, props).

// example
const elFunc = ({ Heading, Text, }, props) => (
  <header>
    {Heading}
    {Text}
  </header>
)
 
const Heading = styled.h2``
const Text = styled.div``
 
const componentsObj = {
  Heading,
  Text
}
 
const SectionHeader = Macro(componentsObj)(elFunc)

Omitting children

For any element not passed as a child to the macro component, the element function will render undefined and React will not render that element. This is useful for conditionally omitting optional children

const macro = Macro({ Icon, Text, CloseButton })
 
const Message = macro({
  Icon,
  Text,
  CloseButton
}) => (
  <Flex p={2} bg='lightYellow'>
    {Icon}
    {Text}
    <Box mx='auto' />
    {CloseButton}
  </Flex>
)

import Message from './Message'
 
const { Text, CloseButton } = Message
 
// Omitting the Icon child element will render Message without an icon.
const message = (
  <Message>
    <Text>{props.message}</Text>
    <CloseButton
      onClick={props.dismissMessage}
    />
  </Message>
)

Props passed to the root component

The second argument passed to the element function allows you to pass props to the root element or any other element within the component.

const macro = Macro({ Image, Text })
 
const Card = macro(({
  Image,
  Text
}, props) => (
  <Box p={2} bg={props.bg}>
    {Image}
    {Text}
  </Box>
))

// example usage
<Card bg='tomato'>
  <Card.Image src='kittens.png' />
  <Card.Text>Meow</Card.Text>
</Card>

Clone Component

To apply default props to the elements passed in as children, use the Clone component in an element function.

import Macro, { Clone } from 'macro-components'
import { Heading, Text } from './ui'
 
const macro = Macro({ Heading, Text })
 
const Header = macro(({ Heading, Text }) => (
  <Box p={2}>
    <Clone
      element={Heading}
      fontSize={6}
      mb={2}
    />
    <Clone
      element={Text}
      fontSize={3}
    />
  </Box>
))

Using a Component Multiple Times

To use the same component twice, give it a unique key in the componentsObject.

import React from 'react'
import Macro from 'macro-components'
import { Heading } from './ui'
 
const macro = Macro({
  Heading: Heading,
  Subhead: Heading
})
 
const Header = macro(({ Heading, Subhead }) => (
  <Box p={2}>
    {Heading}
    {Subhead}
  </Box>
))

<Header>
  <Header.Heading>Hello</Header.Heading>
  <Header.Subhead>Subhead</Header.Subhead>
</Header>

---

Alternatives

To create layout components that are not coupled to specific child components, using props or ordered children is probably a simpler approach.

The solutions below allow you to pass any arbitrary components as props or children.

See this discussion for more.

// using custom props
const MyLayout = ({
  left,
  right
}) => (
  <Flex>
    <Box width={128}>
      {left}
    </Box>
    <Box width={1}>
      {right}
    </Box>
  </Flex>
)
 
<MyLayout
  left={(
    <Image src='kitten.png' />
  )}
  right={(
    <Text>Meow</Text>
  )}
/>

// using ordered children
const Header = props => {
  const [ first, second ] = React.Children.toArray(props.children)
  return (
    <Box p={3}>
      {first}
      {second}
    </Box>
  )
}
 
<Header>
  <Heading>First</Heading>
  <Text>Second</Text>
</Header>

// using a children object
const Header = ({
  children: {
    left,
    right
  }
}) => (
  <Flex>
    <Box>
      {left}
    </Box>
    <Box width={1}>
      {right}
    </Box>
  </Flex>
)
 
<Header>
  {{
    left: (
      <Image src='kitten.png' />
    ),
    right: (
      <Text>Meow</Text>
    )
  }}
</Header>

---

Related

• styled-components
• glamorous
• emotion
• styled-system
• system-components
• MediaObject example based on: The media object saves hundreds of lines of code

MIT License