This error is related to the Webpacker and Babel setup that changed in Webpacker 5.1, so it is related to targets in that targets cause the static elements to be used and the Babel setup has some trouble with that language feature.

it’s possible that some of the directories in the sample code weren’t updated properly, I’ll take a look.

Thanks!

This might be a change in how the released version of Stimulus 2.0 handles implicit properties, but I was getting the same error on line 6. Just removing the line with the property declaration caused the code to work.

// app/javascripts/controllers/day_toggle_controller.ts
import { Controller } from "stimulus"

export default class DayToggleController extends Controller {
  static targets = ["thingToHide"]

  // This was the offending line. Was expecting a different error when commented out, but it worked 
  // thingToHideTarget: HTMLElement

  toggle() {
    console.log('Click! Click! Boom!')
    this.thingToHideTarget.classList.toggle("is-hidden")
  }
}

I’m only on page 37 and don’t know Typescript or Stimulus, so I don’t know if this will cause problems later on.