New Twiddle

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  alert() {
    alert('Oh no! The action bubbled.');
  },
  actions: {
    returnEarly(event) {
      console.log(arguments);
      if (event.target.tagName === 'A' && event.target.href) {
        return;
      }
      this.alert();
    },
    dontReturnEarly() {
      this.alert();
    }
  }
});

templates.application.hbs

<ul>
  <li><a href="https://example.com">No Action</a></li>
  <li onclick={{action "dontReturnEarly"}}><a href="https://example.com">Action without considering link</a></li>
  <li onclick={{action "returnEarly"}}><a href="https://example.com">Return Early</a></li>
  <li onclick={{action "dontReturnEarly"}}><a href="https://example.com" onclick="event.stopPropagation()">Hijack Event</a></li>
</ul>

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"
  }
}