mobx decorators rendering warnings in strict mode

[NBSquare]

I'm currently migrating our team's tooling to use the new 2022.3 decorators. We have a model that looks like the following:

class User {
  @observable accessor username: string;
  @observable accessor creationDate: Date | undefined = undefined;
  
  constructor(username: string, creationDate?: Date) {
    this.username = username;
    this.creationDate = creationDate;
  }
}

In our application, we then construct the model using new User(username, creationDate)
In doing so we get the following error:

[MobX] Since strict-mode is enabled, changing (observed) observable values without using an action is not allowed. Tried to modify: [email protected]

Why are we running into this issue? I see a very similar pattern in the docs

We are using:

• React 18.3.1
• Mobx 6.13.1
• mobx-react 9.1.1

[mweststrate]

How/ where do you construct the new User? Not in an action?

…

On Tue, Jun 24, 2025, 01:30 Nathan ***@***.***> wrote: I'm currently migrating our team's tooling to use the new 2022.3 decorators. We have a model that looks like the following: class User { @observable accessor username: string; @observable accessor creationDate: Date | undefined = undefined; constructor(username: string, creationDate?: Date) { this.username = username; this.creationDate = creationDate; } } In our application, we then construct the model using new User(username, creationDate) In doing so we get the following error: [MobX] Since strict-mode is enabled, changing (observed) observable values without using an action is not allowed. Tried to modify: ***@***.*** Why are we running into this issue? I see a very similar pattern in the docs <https://mobx.js.org/observable-state.html> We are using: - React 18.3.1 - Mobx 6.13.1 - mobx-react 9.1.1 — Reply to this email directly, view it on GitHub <#4565>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBGJZL6PLDOWMWK5TA33FCEZDAVCNFSM6AAAAAB76WE3AOVHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZYGQ4DMMRQGA> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[NBSquare]

We are not constructing the user in an action, and we're calling the constructor from a different context A simplified version of what we're doing:

async function buildUser() {
  let response = await someApiCall();
  return new User(response.username, response.date);
}

said async function is in term called from a useEffect in one of our React components, which is an observer.

[mweststrate]

Ok, turning that into a flow or (run)inAction should suffice

…

On Tue, Jun 24, 2025, 06:08 Nathan ***@***.***> wrote: We are *not* constructing the user in an action, and we're calling the constructor from a different context A simplified version of what we're doing: async function buildUser() { let response = await someApiCall(); return new User(response.username, response.date); } said async function is in term called from a useEffect in one of our React components. — Reply to this email directly, view it on GitHub <#4565 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAN4NBBYGCZQBA6WWV2YRE33FDFLNAVCNFSM6AAAAAB76WE3AOVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGNJVG4ZDQOI> . You are receiving this because you commented.Message ID: ***@***.***>