Define get/set in constructor function

This can be done:

var o = {
  _foo : "bar",
  get Foo() { return _foo; },
  set Foo(value) { _foo = value; }
};

But my code is defined in a constructor function, so I want something like this:

function Something(defaultFoo) {
  var _foo = defaultFoo;
  get Foo() { return _foo; };               // invalid syntax
  set Foo(value) { _foo = value; };         // invalid syntax
}

var something = new Something("bar");
console.log(something.Foo);

That syntax is invalid. Is there some variation that works?