Yeah, that works. Good thinking. But you also need to preserve the Child prototype. Object.assign was introduced in ES6, so you need to also take care of that.

function createObject( prototype ) {
  function Wrapper() {}
  Wrapper.prototype = prototype;
  return new Wrapper();
}
function extend(Child, Parent) {
  var childPrototype = createObject( Parent.prototype );
childPrototype.constructor = Child;
  Child.prototype = Object.assign( childPrototype, Child.prototype );
}
function Animal() {}
Animal.prototype.category = 'ANIMAL';
function Dog() {}
Dog.prototype.kind = 'DOG';
extend(Dog, Animal);
console.log((new Dog()).category); // ANIMAL
console.log((new Dog()).kind); // DOG

BTW, you can also use this var Wrapper = new Function(); but this is really unreliable and unnecessary.