New Twiddle

components.my-component.js

import Ember from 'ember';
import { scheduleOnce } from '@ember/runloop';

export default Ember.Component.extend({
  didInsertElement() {
    this._super(...arguments);
    let input = this.element.querySelector('#my-input');
    scheduleOnce('afterRender', this.input, 'focus');
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  isOpen: false,
  actions: {
    toggleOpen() {
      this.toggleProperty('isOpen');
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<input type="checkbox" id="the-checkbox" value={{isOpen}} onchange={{action "toggleOpen"}}>
<label for="the-checkbox">Show/hide component</label>
{{#if isOpen}}
  {{my-component}}
{{/if}}
<br>
<br>

templates.components.my-component.hbs

<div style="border: 1px solid red; padding: 5px">
<input type="text" id="my-input">
</div>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}