Validate Hex Color Codes (RGB/RGBA)

const hexColorRegex = /^#([A-Fa-f0-9]{3}([A-Fa-f0-9]{1})?|[A-Fa-f0-9]{6}([A-Fa-f0-9]{2})?)$/;

function isValidHexColor(hex) {
  return hexColorRegex.test(hex);
}

console.log(isValidHexColor("#FFF"));     // true
console.log(isValidHexColor("#FFFA"));    // true
console.log(isValidHexColor("#FF00FF"));  // true
console.log(isValidHexColor("#FF00FF00")); // true
console.log(isValidHexColor("#GG0"));     // false
console.log(isValidHexColor("FFF"));      // false (missing #)

How it works: This JavaScript regex validates hex color codes, accommodating various common formats. It starts with an `#` and then allows for two main patterns: either three hexadecimal characters followed by an optional fourth (for RGBA shorthand like `#FFFA`), or six hexadecimal characters followed by an optional two (for full RGBA like `#FF00FF00`). This pattern is highly useful for validating color inputs in UI tools or forms where users specify colors.