Actions/computed

controllers.application.js

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

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  someOtherProp: 0,
  
  someProp: computed('someOtherProp', function() {
    return this.someOtherProp;
  }),

  actions: {
    increment(prop) {
      this.set('someOtherProp', prop + 1);
    },
  },
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>
<h4>Count: {{someOtherProp}}</h4>

<button onclick={{action "increment" someOtherProp}}>
  Increment
</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"
  }
}