Converting between rgb and hex colors in javascript

Recently I've need to be able to convert between rgb and hex colors.

Here's the javascript functions I used.

function hex2Rgba(hexColor, opacity) {
            // Only accepts #123456 format for now
            if (color[0] === '#' && color.length === 7) {

                var r,g,b;
                r = parseInt(color.substring(1,3), 16);
                g = parseInt(color.substring(3,5), 16);
                b = parseInt(color.substring(5,7), 16);

                // 
                return "rgba("+r+","+g+","+b+","+opacity+")";
            }
            return null;
        }

Obviously this is pretty basic, and doesn't support the #123 format.

For converting in the other direction I found this code on stackoverflow..

function rgb2hex(rgb) {
 rgb = rgb.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
 function hex(x) {
  return ("0" + parseInt(x).toString(16)).slice(-2);
 }
 return "#" + hex(rgb[1]) + hex(rgb[2]) + hex(rgb[3]);
}