Questions about using Observables in typescript

[inteja]

I'm still a relative newbie with BJS and typescript. 

I've managed to get observers working in my TS class but I found that I couldn't use "this" instance references within the callback function e.g.

class MyMesh extends BABYLON.Mesh {

  private myMeshChild:BABYLON.Mesh;

  constructor() {

    // Create child mesh and add some animation etc.

    this.myMeshChild.onBeforeRenderObservable.add(function () {
      console.log(this.myMeshChild.rotation);
    }
  }
}

This compiles fine but results in runtime error "Cannot read property 'rotation' of 'undefined'".

But if I instead assign to a local variable first, then it works, e.g.

class MyMesh extends BABYLON.Mesh {

  private myMeshChild:BABYLON.Mesh;

  constructor() {

    // Create child mesh and add some animation etc.

    let myMeshChild = this.myMeshChild;
    this.myMeshChild.onBeforeRenderObservable.add(function () {
      console.log(myMeshChild.rotation);
    }
  }
}

 

I feel like I'm using Observables all wrong in Typescript. I'm wondering what's the best way to pass variables to the callback function from within my TS classes? Also I feel like if I add an observer to a mesh then the callback function should be aware of the context i.e. the mesh object from which it's called and therefore I shouldn't have to also assign objects to local variables before I can refer to them in the function, but maybe I'm expecting too much.

Any pointers on using Observables correctly from within Typescript classes would be most appreciated.

@Nockawa @Deltakosh

[GameMonetize]

Hello you were pretty close

Actually you need to use arrow functions:

class MyMesh extends BABYLON.Mesh {

  private myMeshChild:BABYLON.Mesh;

  constructor() {

    // Create child mesh and add some animation etc.

    this.myMeshChild.onBeforeRenderObservable.add(() => {
      console.log(this.myMeshChild.rotation);
    });
  }
}

 

[Nockawa]

Using the arrow function will guaranty you that you can use "this" inside the function, otherwise "this" is the window object, which is not what you expect/want.

[inteja]

Ah. Thanks so much!