abstract class prototype type has abstract methods even though they are not on the prototype

Bug Report

🔎 Search Terms

abstract, prototype, type

🕗 Version & Regression Information

All versions I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

abstract class AnAbstract {
  public abstract abstractMethod(): void;

  public nonAbstractMethod(): void {
    // do something
  }
}

// no type error - undefined
console.log(AnAbstract.prototype.abstractMethod);
// no type error - false
console.log(AnAbstract.prototype.hasOwnProperty('abstractMethod'));

// defined
console.log(AnAbstract.prototype.nonAbstractMethod);
// true
console.log(AnAbstract.prototype.hasOwnProperty('nonAbstractMethod'));

🙁 Actual behavior

Abstract class prototype has abstract methods in the type

🙂 Expected behavior

Abstract class prototype to have only concrete methods in the type

I have a function that manually define methods based on what's in the prototype, unfortunately when I use an abstract class the type doesn't reflect reality.

If that type cannot change it would be great to be able to do something like:

type NoAbstract<T> = {
  -abstract [key in keyof T]: T[key];
};

Start with the linked TypeScript Playground example and compare the declared abstract method with the runtime prototype behavior. Trace how the type of an abstract class's prototype is formed, then verify that concrete methods remain available while abstract methods do not; the issue is done when the reported example type-checks consistently with runtime reality and relevant regression coverage passes.