index.js

'use strict';

const hexCharacters = 'a-f\\d';
const match3or4Hex = `#?[${hexCharacters}]{3}[${hexCharacters}]?`;
const match6or8Hex = `#?[${hexCharacters}]{6}([${hexCharacters}]{2})?`;
const nonHexChars = new RegExp(`[^#${hexCharacters}]`, 'gi');
const validHexSize = new RegExp(`^${match3or4Hex}$|^${match6or8Hex}$`, 'i');

module.exports = (hex, options = {}) => {
	if (typeof hex !== 'string' || nonHexChars.test(hex) || !validHexSize.test(hex)) {
		throw new TypeError('Expected a valid hex string');
	}

	hex = hex.replace(/^#/, '');
	let alpha = 1;

	if (hex.length === 8) {
		alpha = parseInt(hex.slice(6, 8), 16) / 255;
		hex = hex.slice(0, 6);
	}

	if (hex.length === 4) {
		alpha = parseInt(hex.slice(3, 4).repeat(2), 16) / 255;
		hex = hex.slice(0, 3);
	}

	if (hex.length === 3) {
		hex = hex[0] + hex[0] + hex[1] + hex[1] + hex[2] + hex[2];
	}

	const num = parseInt(hex, 16);
	const red = num >> 16;
	const green = (num >> 8) & 255;
	const blue = num & 255;

	return options.format === 'array' ?
		[red, green, blue, alpha] :
		{red, green, blue, alpha};
};