mobx-react observer don't fires when I set observable

Question

I am trying to create a react application using mobx and typescript. But it doesn\'t work.

I expect the timer to count the seconds. And I see that the event happens a

Answer 1

Are you using MobX 6?

Decorator API changed a little bit from MobX 5, now you need to use makeObservable method inside constructor to achieve same functionality as before:

import { observable, action, makeObservable } from "mobx";

export class TestStore {
    @observable timer = 0;

    constructor() {
      makeObservable(this);
    }

    @action timerInc = () => {
        this.timer += 1;
    };
}

Although there is new thing that will probably allow you to drop decorators altogether, makeAutoObservable:

import { makeAutoObservable } from "mobx";

export class TestStore {
    timer = 0;

    constructor() {
      // Don't need decorators now, just this call
      makeAutoObservable(this);
    }

    timerInc = () => {
        this.timer += 1;
    };
}

More info here: https://mobx.js.org/react-integration.html