Fix class.extend to support class.static and removes mixins

class.js

function Class() {}
Class.extend = extend;
module.exports = Class;

function extend(Subclass, prototype) {
  // Support no constructor
  if (typeof Subclass !== 'function') {
    prototype = Subclass;
    var SuperClass = this;
    Subclass = function() {
      SuperClass.apply(this, arguments);
    };
  }

  Subclass.extend = extend;
  extendStatics(this, Subclass, prototype);

  var descriptors = getDescriptors(prototype);
  descriptors.constructor = { writable: true, configurable: true, value: Subclass };
  Subclass.prototype = Object.create(this.prototype, descriptors);
  return Subclass;
}


// Get descriptors (allows for getters and setters) and sets functions to be non-enumerable
function getDescriptors(object) {
  var descriptors = {};
  if (object) {
    Object.getOwnPropertyNames(object).forEach(function(name) {
      descriptors[name] = Object.getOwnPropertyDescriptor(object, name);
    });
  }
  return descriptors;
}

// Copies static methods over for static inheritance
function extendStatics(Class, Subclass, prototype) {
  var descriptors;

  if (prototype && prototype.static) {
    descriptors = getDescriptors(prototype.static);
    delete prototype.static;
  }

  Subclass.static = Object.create(Class.static || null, descriptors);
}