👀 Views: 62 💬 Answers: 1 📅 Created: 2025-06-16

typescript generics class TypeScript

Could someone explain I'm working on a TypeScript project (version 4.4) where I have a class that utilizes generics with constraints, but I'm running into issues with type resolution that seems inconsistent. I have a base class `Entity<T>` and a derived class `User` which extends `Entity<User>`. However, when I try to use the `getId` method from `Entity`, I'm getting a type behavior that states `Property 'id' does not exist on type 'T'`. Here is the relevant code: ```typescript class Entity<T extends Entity<T>> { protected id: string; constructor(id: string) { this.id = id; } getId(): string { return this.id; } } class User extends Entity<User> { constructor(id: string) { super(id); } } const user = new User('123'); console.log(user.getId()); // This gives an behavior ``` I expected `user.getId()` to return `'123'`, but instead, I get a TypeScript behavior stating that the method `getId` want to be found on type `User`. I've tried adding an explicit return type to the `getId` method as `string`, but the behavior continues. I also attempted to change the constraint on `T` to `any`, but that led to different typing issues downstream. Can anyone guide to understand why this is happening and how I can resolve the type behavior without losing the benefits of the generic constraints? For context: I'm using Typescript on macOS. Has anyone else encountered this? The project is a desktop app built with Typescript. What's the best practice here?