gistfile1.txt

extern class State {
  public static function create(options:State):State;
  @:optional public var route:String;
}

// I am aiming for type safety for something like:

var state = State.create({route:"Hello", somethingRandom: 1});

// If instead I do

extern class State {
  public static function create(options:StateDef):State;
  @:optional public var route:String;
}

typedef StateDef = {
  var route:String;
}

// it works out, but then I can't add any extra dynamic properties and somethingRandom throws an error