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JavaScript

/**
* Get luminance from a HEX color.
*
* @since Twenty Twenty-One 1.0
*
* @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.
*
* @since Twenty Twenty-One 1.0
*
* @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;
}