Allow subclasses to declare overloads of methods

Suggestion

Allow subclasses to declare an overload of a superclass method:

This would be useful with addEventListener() in order to provide the correct event type for an event name:

class MyElement extends HTMLElement {
  declare addEventListener(type: 'my-event', listener: (this: MyElement, ev: MyEvent) => any, options?: boolean | AddEventListenerOptions): void;
}

🔍 Search Terms

Various combinations: addEventListener subclass declare overload method

A lot of issues were returned from queries, I could have missed something.

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

See above. I'm not sure the reason for not allowing declare on methods currently, so hopefully that could be relaxed.

📃 Motivating Example

See above.

Right now you would have to augment the HTMLElementEventNameMap, but that makes events global, which they might not be if they don't bubble.

💻 Use Cases

See above.

Start by investigating TypeScript's handling of declare methods and inherited method overloads. Compare the proposed subclass addEventListener declaration with the current behavior and determine the type-checking rules required. Done should allow the subclass overload without changing emitted JavaScript while preserving compatibility with the superclass method.