Convert hex colour to RGB values, and utility to create a CSS RGBA value from a hex and provided alpha value

hexColorConverter.ts

const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i;
const rgbRegex = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i;

/**
 * Converts a CSS hex value into an RGB array
 */
export const hexToRgb = (hex: string): number[] | null => {
  // Expand shorthand form (e.g. "03F") to full form (e.g. "0033FF")
  const result = rgbRegex.exec(
    hex.replace(shorthandRegex, (_, red: string, grn: string, blu: string) => `${red}${red}${grn}${grn}${blu}${blu}`)
  );

  return result ? result.slice(1).map((tok: string) => parseInt(tok, 16)) : null;
};

/**
 * Convert a CSS hex value into a CSS rgba definition
 */
export const hexToRgba = (hex: string, alpha: number | string): string => {
  const rgb = hexToRgb(hex);

  if (!rgb || !alpha) {
    return "";
  }

  return `rgba(${rgb}, ${alpha})`;
};