function runkit_class_adopt (classname, parentname) {
  // http://kevin.vanzonneveld.net
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // %          note 1: Function can only obtain and set classes from the global context
  // *     example 1: function A () {}
  // *     example 1: A.prototype.methodA = function () {};
  // *     example 1: function B () {}
  // *     example 1: runkit_class_adopt('B', 'A');
  // *     returns 1: true

  if (typeof this.window[classname] !== 'function' || typeof this.window[parentname] !== 'function') {
    return false;
  }

  // Classical style of inheritance
  this.window[classname].prototype = new this.window[parentname](); // Has side effects by calling the constructor!

/*
  // Prototypal completely by reference
  this.window[classname].prototype = parentname.prototype; // By mutual reference!
*/

/*
  // Mixin (deep copy, not by reference)
  var _copy = function (child, parent) {
    var p = '';
    for (p in parent) {
      if (typeof parent[p] === 'object') {
        child[p] = _copy(child[p], parent[p]);
      }
      else {
        child[p] = parent[p];
      }
    }
  };
  _copy(this.window[classname].prototype, this.window[parentname].prototype);
*/

  // Put original constructor property back
  this.window[classname].constructor = this.window[classname];
  return true;
}

function A () {}
A.prototype.methodA = function () {};
function B () {}
runkit_class_adopt('B', 'A');

true