observable.ref and decorate() function

[davidmz]

I am trying to use MobX (5.1) with TypeScript (3.0) but without a decorators syntax. Docs recommends to replace @-directives by decorate(Class, {}) function. There is sample code:

import { decorate, observable } from 'mobx';

class A {
  foo?: object;
}

decorate(A, {
  foo: observable.ref,
});

And this code produces the following TS error in my environment:

Argument of type '{ foo: IObservableDecorator; }' is not assignable to parameter of type '{ prototype?: MethodDecorator | PropertyDecorator | MethodDecorator[] | PropertyDecorator[] | undefined; }'.
  Object literal may only specify known properties, and 'foo' does not exist in type '{ prototype?: MethodDecorator | PropertyDecorator | MethodDecorator[] | PropertyDecorator[] | undefined; }'.

There is obviously something wrong with types but in fact this code works: https://codesandbox.io/s/znyp2x33xx

What am I doing wrong and what is the recommended way to do such things?

[mweststrate]

Does the error go away without '?' Op ma 3 sep. 2018 21:10 schreef Давид Мзареулян <[email protected]>:

…

I am trying to use MobX (5.1) with TypeScript (3.0) but without a decorators syntax. Docs recommends to replace @-directives to decorate(Class, {}) function. There is sample code: import { decorate, observable } from 'mobx'; class A { foo?: object; } decorate(A, { foo: observable.ref, }); And this code produces the following TS error in my environment: Argument of type '{ foo: IObservableDecorator; }' is not assignable to parameter of type '{ prototype?: MethodDecorator | PropertyDecorator | MethodDecorator[] | PropertyDecorator[] | undefined; }'. Object literal may only specify known properties, and 'foo' does not exist in type '{ prototype?: MethodDecorator | PropertyDecorator | MethodDecorator[] | PropertyDecorator[] | undefined; }'. There is obviously something wrong with types but in fact this code works: https://codesandbox.io/s/znyp2x33xx What am I doing wrong and what is the recommended way to do such things? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#1713>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ABvGhAKi1oh6eZ4R_itEdF6nK6zg_s-Lks5uXX63gaJpZM4WX-bx> .

[davidmz]

No, it does not.

I found that the problem is related to the strictFunctionTypes flag in tsconfig.json. This flag is true in my environment, if I set it to false, the error disappears. I made a small test repository to demonstrate this issue: https://github.com/davidmz/mobx-decorate-test.

[davidmz]

Hmm, strictFunctionTypes isn't always working… Looks like TS chooses invalid definition for 'decorate', decorate<T>(object: T, … instead of decorate<T>(clazz: new…, and requires keys of class function as object (i. e. prototype).

[nykula]

Please review pull requests #1711 and #1712, they fix calling decorate with modifiers. This is connected to an older issue, #1448.

[mweststrate]

This changes has been released yesterday, closing the issue