class property decorators initialization

es7-decorator-stuff

    var descriptor = Object.getOwnPropertyDescriptor(Person.prototype, 'born');
    if(typeof descriptor.set === 'function'){
      descriptor.set(_instanceInitializers.born.call(this));
    }
    else if(descriptor.get === undefined && descriptor.set === undefined) {
      var value =  _instanceInitializers.born.call(this);
      descriptor.value =  value === undefined ? descriptor.value : value;
    }
    Object.defineProperty(this, 'born', descriptor);