polished/lib/color/getLuminance.js

A lightweight toolset for writing styles in Javascript.

"use strict";

exports.__esModule = true;
exports["default"] = getLuminance;
var _parseToRgb = _interopRequireDefault(require("./parseToRgb"));
function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { "default": obj }; }
/**
 * 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: ${getLuminance('rgba(58, 133, 255, 1)') >= getLuminance('rgba(255, 57, 149, 1)') ?
 *                             'rgba(58, 133, 255, 1)' :
 *                             'rgba(255, 57, 149, 1)'};
 *
 * // CSS in JS Output
 *
 * div {
 *   background: "#CCCD64";
 *   background: "rgba(58, 133, 255, 1)";
 * }
 */
function getLuminance(color) {
  if (color === 'transparent') return 0;
  var rgbColor = (0, _parseToRgb["default"])(color);
  var _Object$keys$map = Object.keys(rgbColor).map(function (key) {
      var channel = rgbColor[key] / 255;
      return channel <= 0.03928 ? channel / 12.92 : Math.pow((channel + 0.055) / 1.055, 2.4);
    }),
    r = _Object$keys$map[0],
    g = _Object$keys$map[1],
    b = _Object$keys$map[2];
  return parseFloat((0.2126 * r + 0.7152 * g + 0.0722 * b).toFixed(3));
}
module.exports = exports.default;