TypeScript: self-referencing return type for static methods in inheriting classes

Question

With Polymorphic this in TypeScript 1.7, as I discovered here, we can define a method in a class with a return type of this, and automatically, any classes that

Answer 1

This is doable in TypeScript 2.0+. By using an inline { new(): T } type to capture this, you'll get what you wanted:

type Constructor = { new (): T }

class BaseModel {
  static getAll(this: Constructor): T[] {
    return [] // dummy impl
  }

  /**
   * Example of static method with an argument:
   */
  static getById(this: Constructor, id: number): T | undefined {
    return // dummy impl
  }

  save(): this {
    return this // dummy impl
  }
}

class SubModel extends BaseModel {}

const sub = new SubModel()
const savedSub: SubModel = sub.save()

// Behold: SubModel.getAll() returns SubModels, not BaseModel
const savedSubs: SubModel[] = SubModel.getAll()

Note that getAll still expects no arguments with this typing.

For more information, see https://www.typescriptlang.org/docs/handbook/generics.html#using-class-types-in-generics and https://stackoverflow.com/a/45262288/1268016