Mobx Upgrade With Base Classes (v4/5 to 6)

[LogicRoom]

We have some classes....

export class CustomField extends GenericField {
   @observable customProperty
}

class GenericField {
   @observable genericProperty
}

We ran the codemod to upgrade Mobx as per the documentation at..... https://mobx.js.org/migrating-from-4-or-5.html

The codemod simply added

constructor() {
   makeObservable(this);
}

To the base class (not the child class) and came up with the error:

/src/CustomField.ts Transformation error (Cannot read property 'start' of null) TypeError: Cannot read property 'start' of null

We are unsure of what to do next? The documentation is not clear in this regard https://mobx.js.org/migrating-from-4-or-5.html#limitations-of-mobx-undecorate it says if base classes expect arguments (does this mean through the constructor?) the codemod will not work. But it doesn't expect anything, so this statement doesn't make sense and nor does the warning.

If we run the codemod again it adds yet another call to makeObservable in the base class but nothing changes on the child.

Any ideas what the correct way forward is....?

[mweststrate]

Every class that introduces observables needs makeObservable, so that includes the subclass indeed. Op ma 28 dec. 2020 09:30 schreef Logic Room <notifications@github.com>:

…

We have some classes.... export class CustomField extends GenericField { @observable customProperty } class GenericField { @observable genericProperty } We ran the codemod to upgrade Mobx as per the documentation at..... https://mobx.js.org/migrating-from-4-or-5.html The codemod simply added constructor() { makeObservable(this); } To the base class (not the child class) and came up with the error: */src/CustomField.ts Transformation error (Cannot read property 'start' of null) TypeError: Cannot read property 'start' of null* We are unsure of what to do next? The documentation is not clear in this regard https://mobx.js.org/migrating-from-4-or-5.html#limitations-of-mobx-undecorate it says if base classes expect arguments (does this mean through the constructor?) the codemod will not work. But it doesn't expect anything, so this statement doesn't make sense and nor does the warning. If we run the codemod again it adds yet another call to makeObservable in the base class but nothing changes on the child. Any ideas what the correct way forward is....? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#2691>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBDL4FWHU7M566YMGOLSXBF5FANCNFSM4VLZKHLQ> .

[LogicRoom]

Thanks @mweststrate , in that case I think the codemod has a bug?

The documentation says ....

The mobx-undecorate command has to introduce a constructor in classes that do not yet have one. If base class of the constructor expects arguments, the codemod cannot introduce these arguments for the subclass being upgraded, and the super call won't pass them either. You have to fix these manually

Yet our class (GenericField ) does not have a constructor argument in the base class, so in that case there is no reason the codemod cannot create one in the subclass?

Also the warning says... 'Transformation error (Cannot read property 'start' of null)' which isn't clear what the problem is?

[mweststrate]

The codemod is a best effort, not a guaranteed correct / complete conversion, and many things can influence its results, for example certain Babel syntax extensions might make the file unparsable for the codemod. If you think a case is missing that should be supported, please PR a unit test with a reproduction. Op ma 28 dec. 2020 11:14 schreef Logic Room <notifications@github.com>:

…

Thanks @mweststrate <https://github.com/mweststrate> , in that case I think the codemod has a bug? The documentation says .... *The mobx-undecorate command has to introduce a constructor in classes that do not yet have one. If base class of the constructor expects arguments, the codemod cannot introduce these arguments for the subclass being upgraded, and the super call won't pass them either. You have to fix these manually* Yet our class (GenericField ) does not have a constructor argument in the base class, so in that case there is no reason the codemod cannot create one in the subclass? Also the warning says... 'Transformation error (Cannot read property 'start' of null)' which isn't clear what the problem is? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#2691 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBG3UO7JCNH4LE7F54LSXBSCRANCNFSM4VLZKHLQ> .

[LogicRoom]

Hi @mweststrate we are doing a significant upgrade with a client and also use Mobx in our UI architecture training. As soon as we finish this upgrade we will look at putting a PR in for this particular issue. Thanks!