StackOverflow fn template helper

components.my-component\.js

import Component from '@glimmer/component';
import { action } from '@ember/object';

export default class extends Component {
  animals = ["dog", "cat"];

  @action
  updateAnimal(animal, event) {
    const { value } = event.target;
    window.alert(`Changed text for animal ${animal} to ${value}`);
  }
}

controllers.application\.js

import Controller from '@ember/controller';

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<br>
<MyComponent />

templates.components.my-component\.hbs

{{#each this.animals as |animal|}}
    <textarea
        value={{animal}}
        {{on "focusout" (fn this.updateAnimal animal)}}
    />
{{/each}}

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"
  }
}