code: function addStatics(statics, Subclass) {
  
    // static method inheritance (including `extend`)
    Object.keys(statics).forEach(function(key) {
      var descriptor = Object.getOwnPropertyDescriptor(statics, key);
      if (!descriptor.configurable) return;
  
      Object.defineProperty(Subclass, key, descriptor);
    });
  }
docs: Copies static methods over for static inheritance