Component's event subscriber resolves callback on subscription

[TitouanGisle]

Description

It seems to me that when a subscriber to an event is created on a component, the callback to this subscriber is instantaneously resolved if said component had previously fired the event.

Context

In my application, I tried to implement a button to create a sectionPlane from a surface :

• my application fires the 'picked' event on the Viewer's SectionPlanePlugin when a element is clicked in the Scene:

  handleSelectionClick(pickResult = null) {
  
      if (!pickResult) {
          return;
      }
  
      console.log('Firing "picked" event');
      this.sectionPlanesPlugin.fire('picked', pickResult);
      
      // Do other stuff related to picking viewer elements
  }

• When my user clicks the "create a section plane from a surface" button, I create a subscriber to the SectionPlanePlugin 'picked' event, using the once() function :

  prepareSectionPlaneFromSurface()
  {
      this.sectionPlanesPlugin.once('picked', this.createSectionPlaneFromSurface);
      console.log("Ready to pick surface");
  }

• The callback to this subscriber creates a SectionPlane :

  createSectionPlaneFromSurface(pickResult)
  {
      console.log("Creating plane from picked surface");
      let plane = this.sectionPlanesPlugin.createSectionPlane({pos: pickResult.worldPos, dir: pickResult.worldNormal});
      this.sectionPlanesPlugin.showControl(plane.id);
  }

Current behavior

• When clicking the "create a section plane from a surface" button for the first time, then clicking the model, a section plane is successfully created.
• When clicking the "create a section plane from a surface" button a second time, a section plane is immediately created, and another section plane is created when the model is clicked.
• On a fresh Viewer/SectionPlanePlugin, if the user clicked a model, and a 'picked' event was fired, a section plane is immediately created when the user clicks the "create a section plane from a surface" button.

Expected behavior

Resolving the callback to a subscriber on its creation if the event is "already" in the Component seems like a strange behavior to me.

Local correction

I managed to correct this behaviour by deleting the registered 'picked' event from the SectionPlanesPlugin :

    prepareSectionPlaneFromSurface()
    {
        delete this.sectionPlugin._events.picked;

        this.sectionPlugin.once('picked', this.createSectionPlaneFromSurface);
    }

** Xeokit Version :**
2.6.69

Desktop :

• OS: Win11
• Browser: Firefox