ModalsAreDifficult

components.my-form.js

import Ember from 'ember';

export default Ember.Component.extend({
  
});

components.my-modal.js

import Ember from 'ember';

export default Ember.Component.extend({
  classNames: ['modal'],
  actions: {
    closeModal() {
       this.$().removeClass('visible');
    }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  actions: {
    openModal() {
       Ember.$('.modal').addClass('visible');
    }
  }
});

styles.app.css

body {
  margin: 12px 16px;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
  font-size: 12pt;
}

.modal {
  display: none;
}

.modal.visible {
  display:block;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

<button type="button" {{action "openModal"}}>Open  Modal</button>
{{my-modal}}

templates.components.my-form.hbs

{{yield}}

templates.components.my-modal.hbs

<h2>I am a modal</h2>
{{my-form}}
<button type="button" {{action "closeModal"}}>Close me</button>

twiddle.json

{
  "version": "0.10.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.7.0",
    "ember-data": "2.7.0",
    "ember-template-compiler": "2.7.0"
  },
  "addons": {}
}