New Twiddle

components.camel-case-to-undersocre-converter.js

import Ember from 'ember';

export default Ember.Component.extend({
  input: '',
  output: "",
  spaceReplacement: "{+}",
  newLine: "\n",
  inputObserver: Ember.observer('input', function() {
    const input = this.get('input');
    const newLine = this.get('newLine');
    const spaceReplacement = this.get('spaceReplacement');
    let lines = input.split(newLine);
    lines = lines.map((line)=>{
    	return String(line)
        .replace(/ /gi,spaceReplacement)
        .underscore()
        .split(spaceReplacement)
        .join(' ');
    });
  	this.set('output', lines.join(newLine));

  })
});

components.tools-list.js

import Ember from 'ember';

export default Ember.Component.extend({
  tool: null,
  actions: {
   	 setComponent(name) {
     		this.set('tool',name);
     }
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'String Convert Tools'
});

styles.app.css

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

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
{{tools-list}}
<br>
<br>

templates.components.camel-case-to-undersocre-converter.hbs

{{yield}}

input:
<br>
{{textarea value=input}}
<br>
output:
<br>
{{textarea value=output}}

templates.components.tools-list.hbs

{{yield}}
<ul>
<li onclick={{action 'setComponent' 'camel-case-to-undersocre-converter'}} data-component="camel-case-to-undersocre-converter">CamelCase to Underscore</li>

</ul>

{{#if tool}}
{{component tool}}
{{else}}
<span>no tool selected</span>
{{/if}}

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}