Private class members aren't really private in TypeScript. What is the right solution?

PrivateFoo.js

function Base() {
  var foo = 0;
  return {
    greet: function () {
      ++foo;
      return "Hello";
    },
    fly: function() {
      return "Flying";
    }
  }
}

function Special() {
  var foo = 0;
  var r = new Base();
  r.greet = function () {
    ++foo;
    return "Hola";
  }
  return r;
}

PrivateFoo.ts

class Base {
  private foo = 0;
  greet() {
    ++this.foo;
    return "Hello";
  }
  fly() {
    return "Flying";
  }
}

class Special extends Base {
  private foo = 0;
  greet() {
    ++this.foo;
    return "Hola";
  }
}

Typescript is an EcmaScript#Next superset and ES not have a specification to private accessors in classes.
Remember TS only add Types and syntax sugar for types, checking this in compile time and remove all types from JS compiled. Like BabelJS, TS does not change ES specification.

If you need to report these members are private to js consumers, maybe you can follow jQuery Widget private member standard.

eg:

class Base {
  private _foo = 0;
  greet() {
    ++this._foo;
    return "Hello";
  }
  private _fly() {
    return "Flying";
  }
}