daijinara said over 3 years ago on Deeper Dive into StimulusJS :
For those seeking to integrate select2, add this code below:

initialize() {
    console.log('hello from city-selector controller')

    $("#state_id, #county_id").on('select2:select', function () {
      let event = new Event('change', { bubbles: true }) // fire a native event
      this.dispatchEvent(event);
    });

    this.check_forms()    
  }