New Twiddle

components.my-component.js

import Component from '@ember/component';
import { computed } from '@ember/object';
import { copy } from '@ember/object/internals';

export default Component.extend({
  
  data: null,
  
  dataWithExtra: computed('data.{a,b,c}', {
    get() {
      let newData = copy(this.get('data'));
      newData['d'] = 'four';
      return newData;
    }
  }),
  
  actions: {
  	updateA(value) {
    	this 
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  data: {
  	a: 'one',
    b: 'two',
    c: 'three'
  },
  
  actions: {
  	updateData() {
    	this.set('data', {
        a: 'four',
        b: 'five',
        c: 'six'
      });
    },
    
    updateJustA() {
     	this.set('data.a', 'new updated A!'); 
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
{{data.a}}
<br>
<br>
{{data.b}}
<br>
<br>
{{data.c}}
<br>
<br>
{{my-component data=data}}
<br>
<br>
<button {{action "updateData"}}>Update Data</button>
<button {{action "updateJustA"}}>Update Just A</button>

templates.components.my-component.hbs

{{input type="text" value=dataWithExtra.a on-input=(mut dataWithExtra.a)}}

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"
  }
}