array

components.a-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  myArray: Ember.A(),
});

components.b-component.js

import Ember from 'ember';
import { readOnly } from '@ember/object/computed'
import AComponent from './a-component'

export default AComponent.extend({
  firstObject: readOnly('myArray.firstObject'),
  actions: {
    pushArray() {
      this.myArray.pushObject('a');
    }
  }
});

controllers.application.js

import Ember from 'ember';

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
{{a-component}}
<br>
<br>
{{b-component}}
<br>
<br>

templates.components.a-component.hbs

{{#each myArray as |a|}}
	{{a}}
{{/each}}

templates.components.b-component.hbs

{{#each myArray as |a|}}
	{{a}}
{{/each}}
<br>
<button {{action 'pushArray'}}>Push</button>

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"
  }
}