On Change textarea

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  changesCount: 0,
  
  actions: {
  	onChange() {
    	this.set('changesCount', this.changesCount + 1);
    }
  }
});

templates.application.hbs

Changes saved: {{changesCount}}
<br/>
<br/>
{{textarea change=(action 'onChange')}}

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.8.0",
    "ember-data": "2.8.0",
    "ember-template-compiler": "2.8.0",
    "ember-testing": "2.8.0"
  },
  "addons": {}
}