Javascript RGB(A) string conversion functions.

rgba.js

/**
  * Parse an rgb or rgba string like 'rgb(67, 216, 89)' or 'rgba(245, 156, 8, 178)'
  * to array of integers in the order.
  * Credit: http://stackoverflow.com/questions/10970958/get-a-color-component-from-an-rgb-string-in-javascript
  **/
 function parse_rgb_string(rgb) {
    rgb = rgb.replace(/[^\d,]/g, '').split(',');
    return rgb;
 }
 
 /**
 * Create and hexadecimal string corresponding to given deciman number.
 **/
 function dec_to_hex_string(dec, length) {
    var hex = dec.toString(16).toUpperCase();
    if (hex.length < length) {
        hex = new Array( length - hex.length + 1 ).join( '0' ) + hex;
    }
    return hex;
}
function rgba_to_hex_string(rgb_string, alpha_percentage) {
    var rgb_array = parse_rgb_string(rgb_string);
    if (typeof alpha_percentage !== 'undefined') {
        var alpha = 255 * alpha_percentage / 100;
        alpha = Math.floor(alpha);
        // Apply alpha value replacing existing if there.
        rgb_array[3] = alpha;
    }
    var hex_string = '';
    for( var i = 0; i < rgb_array.length; i++) {
        hex_string += dec_to_hex_string(rgb_array[i], 2);
    }
    return '#' + hex_string;
}