ViewModel trigger.on() callbacks are registered but never invoked

[JeppeP]

Summary

When using the ViewModel Instance API to observe triggers via trigger.on(callback), callbacks are correctly registered but never invoked when the trigger fires.

Environment

• Runtime: @rive-app/canvas v2.32.2
• Browser: Chrome 131 (also tested in Safari)
• OS: macOS

Steps to Reproduce

1. Create a .riv file with a ViewModel containing a trigger property
2. Set up a Listener in Rive that fires the trigger on click
3. In JavaScript, observe the trigger:

javascript
const rive = new Rive({
    src: 'file.riv',
    canvas: document.querySelector('canvas'),
    stateMachines: ['StateMachine'],
    autoBind: true,
    onLoad: () => {
        const vmi = rive.viewModelInstance;
        const trigger = vmi.trigger('myTrigger');
        
        console.log('callbacks before:', trigger.callbacks?.length); // 0
        
        trigger.on(() => {
            console.log('Trigger fired!'); // Never called
        });
        
        console.log('callbacks after:', trigger.callbacks?.length); // 1
    }
});

4. Click the element that should fire the trigger

Expected Behavior

The callback passed to trigger.on() should be invoked when:

• The trigger fires from a Rive Listener interaction
• trigger.trigger() is called from JavaScript

Actual Behavior

• Callback is registered (callback count increases from 0 to 1)
• Callback is never invoked
• Manually calling trigger.callbacks.forEach(cb => cb()) does work

Workaround

Currently using onStateChange to detect state transitions as a fallback for navigation triggers.

Additional Context

• The .on() method exists and accepts callbacks
• Internal callbacks array is populated correctly
• The invocation mechanism appears to be broken

Happy to provide a minimal reproduction repo if needed.

[zplata]

Hi @JeppeP - apologies for the late reply on this, but if you bump to the latest verison of the JS runtime, do you still run into this issue? Likely there may have been fixes during the time this was reported. I'm not able to repro with the steps you provided. But if you are still able to on the latest version, would you mind providing a CodeSandbox/codepen for us to dig into?