🐞 Describe the Bug

Beginning with ember v5.12 the error handing is not helpful when you forget to create the pass function to on modifier.

🔬 Minimal Reproduction

Create a hbs file with this content:

<div {{on "click" this.myfunction}}></div>

Minimal reproduction: https://github.com/mkszepp/ember-missing-action-function

😕 Actual Behavior

If you forget to create the function in js/ts you will get this error:
Error in Firefox:
Uncaught TypeError: userProvidedCallback is undefined

Error in Chrome:
Uncaught TypeError: Cannot read properties of undefined (reading 'bind')

🤔 Expected Behavior

We should bring back better error handling like it was in <= v5.11

Uncaught Error: You must pass a function as the second argument to the `on` modifier; you passed undefined. While rendering:

this.myfunction

Possible error position

While looking the commit it looks like the error was introduced here
2d9fc01#diff-301b4fe274bd34f5552c35fc1f58078575896ba487df721bed939eb1d0fe9891R75

The answer of @NullVoxPopuli was see

oofta -- that check stuff in general is supposed to be stripped during glimmer-vm publish.

thank you for finding and reporting this!!!

🌍 Environment

• Ember: 5.12.0+
• Ember-CLI: 5.12.0+
• Node.js/pnpm: v20 / v9
• OS: Linux / WIndows
• Browser: Firefox / Chrome

Original post