ember-autosize-textarea

components.textarea-autosize.js

import Ember from 'ember';

export default Ember.TextArea.extend({
  rows: 1,
  input() {
    this.resizeTextArea();
  },
  resizeTextArea() {
    let el = this.get('element');
    el.style.height = 'auto';
    el.style.height = el.scrollHeight + 'px';
  },
  didInsertElement() { 
    this._super(...arguments); 
    this.resizeTextArea(this.get('element'));
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle'
});

styles.app.css

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

textarea {
  box-sizing: border-box;
  resize: none;
  /**
   * The same can be achived by setting offset on didInsertElement():
   * ```
   *  const el = this.get('element');
   *  this.set('offset', el.offsetHeight - el.clientHeight);
   * ```
   * and adding it to calculated height:
   * ```
   * el.style.height = el.scrollHeight + this.get('offset') + 'px';
   * ```
   */
  overflow-y: hidden;
}

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<h4>Auto size textarea component</h4>
{{textarea-autosize value="News aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation siteNews aggregation site"}}
<br>
<br>

twiddle.json

{
  "version": "0.10.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.6.0",
    "ember-data": "2.6.1",
    "ember-template-compiler": "2.6.0"
  },
  "addons": {}
}