New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'EmberSVG',
  circleRadius: 10,
  actions: {
  	changeRadius(amount) {

    	const currentRadius = this.get('circleRadius');
      console.log('change radous', amount, currentRadius);
      this.set('circleRadius', currentRadius + amount);
    }
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<button {{action "changeRadius" 1}}>+</button>
<button {{action "changeRadius" -1}}>-</button>
<svg viewBox="0 0 300 100">
	<circle cx="50" cy="50" r="{{circleRadius}}" fill="grey" />
</svg>
{{outlet}}
<br>
<br>

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"
  }
}