/**
 * Usage  var you = 'hello you guys'.between('hello ',' guys');
 * you = 'you';
 */
String.prototype.between = function(prefix, suffix) {
  s = this;
  var i = s.indexOf(prefix);
  if (i >= 0) {
    s = s.substring(i + prefix.length);
  }
  else {
    return '';
  }
  if (suffix) {
    i = s.indexOf(suffix);
    if (i >= 0) {
      s = s.substring(0, i);
    }
    else {
      return '';
    }
  }
  return s;
}

http://userscripts.org/scripts/review/35396

Get String between a Prefix String and a Suffix String

JavaScript