WordPress/wp-content/themes/twentytwentyone/assets/js/customize-helpers.js

/**
 * Get luminance from a HEX color.
 *
 * @param {string} hex - The hex color.
 *
 * @return {number} - Returns the luminance, number between 0 and 255.
 */
function twentytwentyoneGetHexLum( hex ) { // jshint ignore:line
	var rgb = twentytwentyoneGetRgbFromHex( hex );
	return Math.round( ( 0.2126 * rgb.r ) + ( 0.7152 * rgb.g ) + ( 0.0722 * rgb.b ) );
}

/**
 * Get RGB from HEX.
 *
 * @param {string} hex - The hex color.
 *
 * @return {Object} - Returns an object {r, g, b}
 */
function twentytwentyoneGetRgbFromHex( hex ) {
	var shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i,
		result;

	// Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF").
	hex = hex.replace( shorthandRegex, function( m, r, g, b ) {
		return r.toString() + r.toString() + g.toString() + g.toString() + b.toString() + b.toString();
	} );

	result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec( hex );
	return result ? {
		r: parseInt( result[1], 16 ),
		g: parseInt( result[2], 16 ),
		b: parseInt( result[3], 16 )
	} : null;
}