Returns all the characters found in one string but not the other.
@param {String} s The string to operate on.
@param {String} other The string to compute the difference against.
@return {String} A difference string.
function differenceFromString (s, other) {
                    if(typeof other !== 'string' || typeof s !== 'string') return s;
                    var sarr = s.split(''), oarr = other.split('');
                    return libs.array.difference(sarr, oarr).join('');
                }