Computed Property Set/Get

components.my-component.js

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

export default Ember.Component.extend({
  myProp: computed({
    // Returns a default value when the component isn't given a myProp property.
    get() { return 'No Prop'; },
    
    // Returns a default value if val is undefined.
  	set(key, val) { return val === undefined ? 'No Prop' : val; }
  })
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

templates.application.hbs

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

Does not have myProp passed in.
{{my-component}}
<br>
myProp is passed an "undefined" value.
{{my-component myProp=(if foo "true Prop")}}
<br>

myProp is passed a string.
{{my-component myProp="Has Prop"}}

templates.components.my-component.hbs

My Prop: {{myProp}}

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"
  }
}