Ember.js – Purpose of decorator `@action`

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';

export default class ApplicationController extends Controller {
  prop = 'the prop';

  @action
  withAction() {
    // `@action` binds `this` to the method
    alert(this.prop)
  }
  
  withoutAction() {
    // `this` does not exist
    alert(this.prop)
  }
}

templates.application\.hbs

<button {{on "click" this.withAction}}>With @action</button>

=> alert() displayed.

<hr>

<button {{on "click" this.withoutAction}}>Without @action</button>

=> checkout the explicit error in the console

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}