polished
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A lightweight toolset for writing styles in Javascript.
64 lines (55 loc) • 1.9 kB
Flow
// @flow
import getValueAndUnit from './getValueAndUnit'
import PolishedError from '../internalHelpers/_errors'
const defaultFontSize = 16
function convertBase(base: string | number): number {
const deconstructedValue = getValueAndUnit(base)
if (deconstructedValue[1] === 'px') {
return parseFloat(base)
}
if (deconstructedValue[1] === '%') {
return (parseFloat(base) / 100) * defaultFontSize
}
throw new PolishedError(78, deconstructedValue[1])
}
function getBaseFromDoc(): number {
/* eslint-disable */
/* istanbul ignore next */
if (typeof document !== 'undefined' && document.documentElement !== null) {
const rootFontSize = getComputedStyle(document.documentElement).fontSize
return rootFontSize ? convertBase(rootFontSize) : defaultFontSize
}
/* eslint-enable */
/* istanbul ignore next */
return defaultFontSize
}
/**
* Convert rem values to px. By default, the base value is pulled from the font-size property on the root element (if it is set in % or px). It defaults to 16px if not found on the root. You can also override the base value by providing your own base in % or px.
* @example
* // Styles as object usage
* const styles = {
* 'height': remToPx('1.6rem')
* 'height': remToPx('1.6rem', '10px')
* }
*
* // styled-components usage
* const div = styled.div`
* height: ${remToPx('1.6rem')}
* height: ${remToPx('1.6rem', '10px')}
* `
*
* // CSS in JS Output
*
* element {
* 'height': '25.6px',
* 'height': '16px',
* }
*/
export default function remToPx(value: string | number, base?: string | number): string {
const deconstructedValue = getValueAndUnit(value)
if (deconstructedValue[1] !== 'rem' && deconstructedValue[1] !== '') {
throw new PolishedError(77, deconstructedValue[1])
}
const newBase = base ? convertBase(base) : getBaseFromDoc()
return `${deconstructedValue[0] * newBase}px`
}