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A lightweight toolset for writing styles in Javascript.
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Flow
// @flow
import parseToRgb from './parseToRgb'
/**
* Returns a number (float) representing the luminance of a color.
*
* @example
* // Styles as object usage
* const styles = {
* background: getLuminance('#CCCD64') >= getLuminance('#0000ff') ? '#CCCD64' : '#0000ff',
* background: getLuminance('rgba(58, 133, 255, 1)') >= getLuminance('rgba(255, 57, 149, 1)') ?
* 'rgba(58, 133, 255, 1)' :
* 'rgba(255, 57, 149, 1)',
* }
*
* // styled-components usage
* const div = styled.div`
* background: ${getLuminance('#CCCD64') >= getLuminance('#0000ff') ? '#CCCD64' : '#0000ff'};
* background: ${getLuminance('rgba(58, 133, 255, 1)') >= getLuminance('rgba(255, 57, 149, 1)') ?
* 'rgba(58, 133, 255, 1)' :
* 'rgba(255, 57, 149, 1)'};
*
* // CSS in JS Output
*
* div {
* background: "#CCCD64";
* background: "rgba(58, 133, 255, 1)";
* }
*/
export default function getLuminance(color: string): number {
if (color === 'transparent') return 0
const rgbColor: { [string]: number } = parseToRgb(color)
const [r, g, b] = Object.keys(rgbColor).map(key => {
const channel = rgbColor[key] / 255
return channel <= 0.03928 ? channel / 12.92 : ((channel + 0.055) / 1.055) ** 2.4
})
return parseFloat((0.2126 * r + 0.7152 * g + 0.0722 * b).toFixed(3))
}