Null attr demo

components.test-component.js

import Ember from 'ember';
import { computed, get } from '@ember/object';

export default Ember.Component.extend({
  baz: computed('foo', {
    get() {
      alert(get(this, 'foo'));
    }
  })
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  bar: 'Some text',
  
  actions: {
    changeToNull() {
      this.set('bar', null);
    },
    changeToUndefined() {
      this.set('bar', undefined);
    },
    changeToString() {
      this.set('bar', 'Some text');
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

{{test-component foo=bar}}

<button onclick={{action "changeToNull"}}>Change to null</button>
<button onclick={{action "changeToUndefined"}}>Change to undefined</button>
<button onclick={{action "changeToString"}}>Change to text</button>

templates.components.test-component.hbs

{{baz}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}