forward.js

function Bar() {}

Bar.prototype.foo = function () {
  console.log('Bar#foo called');
};

Bar.prototype.bar = function (arg) {
  console.log(this);
  console.log('Bar#bar called with ' + arg);
};

function Foo() {}

var Forwardble = {
  forward: function() {
    var methods = Array.prototype.slice.call(arguments);
    var sender = this;

    return {
      to: function(receiver) {
        for (var i=0; i<methods.length; i++) {
          (function() {
            var method = methods[i];
            sender[method] = function() {
              receiver[method].apply(receiver, arguments);
            };
          })();
        }
      }
    }
  }
}

// Extend?
Foo.prototype.forward = Forwardble.forward;

// ----------------------------------------------------------------------------

var foo = new Foo();
var bar = new Bar();

foo.forward('foo', 'bar').to(bar);

foo.foo();
foo.bar('baz!');