Strange typescript issue

[bellostom]

Hi

I get the attached error from typescript when using observe. However, it works correctly in the browser, there is no error.
Any ideas why? based on the error, it seems that I am not using it correctly, although I have been using observe this way for a long time is pure JS projects.
I am now porting to TS and run into this.
Thanks for any feedback

[kubk]

Hi @bellostom
In TypeScript keyof Type skips private/protected fields:

class Test {
  public a = 1;
  private b = 1;
}

type Props = keyof Test; // Only 'a', not 'a' | 'b'

As a workaround you can change protected to public. As a solution I'd suggest to replace observe with reaction or autorun as recommended in docs: https://mobx.js.org/intercept-and-observe.html#intercept--observe-

Note for Mobx maintainers: The issue can be solved by introducing AdditionalKeys on observe the same way it was done for makeObservable/makeAutoObservable:

• mobx/packages/mobx/src/api/makeObservable.ts

  Line 26 in 1174004

  export function makeObservable<T extends object, AdditionalKeys extends PropertyKey = never>(

• https://mobx.js.org/observable-state.html#limitations

But since observe is low level utility and it is not recommended to use, I wouldn't add this TS hack to Mobx repo again.

[bellostom]

Thanks @kubk for the comprehensive answer.
I switched to reaction
I would never have thought that the visibility was the culprit