defineProperties.js

function defineProperties (aTarget, aSource) {
  var key, desc;
  for (key of Object.getOwnPropertyNames(aSource)) {
    desc = Object.getOwnPropertyDescriptor(aSource, key);
    desc.enumerable = false;
    Object.defineProperty(aTarget, key, desc);
  }
  return aTarget;
}

// example

function Foo(){}
defineProperties(Foo.prototype, {
  getName: function(){ return this.name; },
});

function Bar(){}
Bar.prototype = defineProperties(Object.create(Foo.prototype), {
  setName: function(val) { this.name = val; },
});