Returns only the characters common to both strings
@param {String} s The string to operate on.
@param {String} other The string to compute the intersection against.
@return {String} The intersection between the two strings.
function intersectString (s, other) {
                    if(typeof other !== 'string' || typeof s !== 'string') return s;
                    var sarr = s.split(''), oarr = other.split('');
                    return libs.array.intersect(sarr, oarr).join('');
                }