TS1267

Property 'isStable' cannot have an initializer because it is marked abstract.

Broken Code ❌

abstract class Base {
  abstract isStable: boolean = true;
}

This error occurs because abstract properties in TypeScript cannot have initializers. Abstract properties only declare the type and must be implemented in derived classes.

Fixed Code ✔️

Remove the initializer from the abstract property and initialize it in the derived class:

abstract class Base {
  abstract isStable: boolean;
}
 
class Derived extends Base {
  isStable: boolean = true;
}
 
const derived = new Derived();
console.log(derived.isStable);