With reference to my code below, I am trying to create a Map<string, Function> (eventHandlerMap in the code below) such that each of its keys is a string from (PortalEvent in the code below) Union type. The value of each property should be a function that must return an object of specific type (in this example one of UserComment or Author).

Objectives:

1. Anytime a new key is added to PortalEvent, a handler function must be defined and eventHandlerMap should be updated.

2. Anytime Author or UserComment type is changed the above, the respective handler should be changed for new/removed properties.

If it helps the types PortalEvent, UserComment and Author are 3rd-party library maintained types and I want to be able to update my code whenever a new version of 3rd-party library is used in the project.

Here is the code I have come up: Playground Link

// Typescript Version 5.1.6

// Code for which I have no control over 
// -------------------------------------

type PortalEvent = 'comment_created' | 'author_updated';

type UserComment = {
  id: string;
  content: string;
}

type Author = {
  id: string;
  name: string;
  country: string
}


// Code that I can change
// ----------------------

// Define the types necessary for defining object eventHandlerMap
type HandlerReturnType = {
  'comment_created': UserComment,
  'author_updated': Author,
}

type HandlerArgType = {
  'comment_created': { arg1: number, arg2: string; },
  'author_updated': { arg1: string },
}

type THandlerMap<A extends {[j in PortalEvent]: unknown}, R extends {[j in PortalEvent]: unknown}> = {
  [key in PortalEvent]: (arg: A[key]) => R[key] ;
};

// Define the Event handler map
const eventHandlerMap: THandlerMap<HandlerArgType, HandlerReturnType> = {
  'comment_created': commentCreatedHandler,
  'author_updated': authorUpdatedHandler,
}


function commentCreatedHandler(args: HandlerArgType['comment_created']): UserComment {
  let id: string = '', content: string = '';

  // ... code to initialize id and content properties

  return {
      id,
      content,
  };
}

function authorUpdatedHandler(args: HandlerArgType['author_updated']): Author {
  let id: string = '', name: string = '', country : string = '';

  // ... code to initialize id, name and country properties

  return {
      id,
      name,
      country
  };
}

The code above achieves the listed objectives. Is there a better way of doing this?