Extend (subclass) native Date

example.js

var date = new MyDate(2015, 5, 18)
console.log(date instanceof Date) //true
console.log(date instanceof MyDate) //true
console.log(Object.prototype.toString.call(date)) //[object Date]
console.log(date.foo()) //bar
console.log('' + date) //Thu Jun 18 2015 00:00:00 GMT-0700 (PDT)

MyDate.js

function MyDate(a, b, c, d, e, f, g) {
  var date;
  switch (arguments.length) {
    case 0:
      date = new Date();
      break;
    case 1:
      date = new Date(a);
      break;
    case 2:
      date = new Date(a, b);
      break;
    case 3:
      date = new Date(a, b, c);
      break;
    case 4:
      date = new Date(a, b, c, d);
      break;
    case 5:
      date = new Date(a, b, c, d, e);
      break;
    case 6:
      date = new Date(a, b, c, d, e, f);
      break;
    default:
      date = new Date(a, b, c, d, e, f, g);
  }
  // note: use `Object.setPrototypeOf` instead of __proto__ to be truly standards-compliant
  date.__proto__ = MyDate.prototype;
  return date;
}

MyDate.prototype.__proto__ = Date.prototype;

MyDate.prototype.foo = function() {
  return 'bar';
};

This approach seems to be the best of the various workarounds I've seen (wrapping Date class, creating class with similar API, etc). It works in IE9+ and all modern JS engines including Node (basically any JS engine that supports modifying the proto chain). Anyone see any drawbacks to this approach?