What is the correct way to add functionality to an object and describe it in jsdoc?

Question

JavaScript

There is a file with the following structure

var API = (function(){
 ....
   return {
      method1: function(){...},
      method2: function(){...},
 ...
   };

})();

All methods are documented with jsdoc. Wanting to expand the functionality, I wrote my method in a separate file. In the Visual Studio Code editor, this method is not visible in the API object. Can anything be done?
API.myMethod = function(){...};