styled-apply-when-truthy

A small utility function for applying some CSS string only when a given prop is truthy.

// This...
${props => props.color ? `color: ${props.color};` : ''}

// can be written as...
${applyWhenTruthy('color', val => `color: ${val};`)}

// Or this...
import { availableColors } from 'my-theme'
${props => props.color ? `color: ${availableColors[props.color]};` : ''}

// can be written as...
import { availableColors } from 'my-theme'
${applyWhenTruthy('color', val => `color: ${availableColors[val]};`)}

When there are several rules like this in a component, I find that the implementation of a styled-component is easier to read if you call applyWhenTruthy outside of the tagged template literal.

For example the following text component that has props for bold, inline, and size.

import styled from 'styled-components'
import { fontSizes, lineHeights } from 'my-theme'

const Text = styled.p`
  ${props => props.bold ? 'font-weight: bold' : ''};
  ${props => props.inline ? 'display: inline' : ''}
  ${props => props.size ? `font-size: ${fontSizes[size]}` : ''};
  ${props => props.size ? `line-height: ${lineHeights[size]}` : ''};
`

Could be rewritten as:

import styled from 'styled-components'
import applyWhenTruthy from 'apply-when-truthy'
import { fontSizes, lineHeights } from 'my-theme'

const propsToBold = applyWhenTruthy(
  'bold',
  _ => 'font-weight: bold;'
)
const propsToDisplay = applyWhenTruthy(
  'inline',
  _ => 'display: inline;'
)
const propsToFontSize = applyWhenTruthy(
  'size',
  val => `font-size: ${fontSizes[val]};`
)
const propsToLineHeight = applyWhenTruthy(
  'size',
  val => `line-height: ${lineHeights[val]};`
)

const Text = styled.p`
  ${propsToBold}
  ${propsToDisplay}
  ${propsToFontSize}
  ${propsToLineHeight}
`

This made the code longer, but it cleans up the tagged template literal that defines our Text component which I find nice :)