Ember-Bootstrap + Ember-AutoResize https://stackoverflow.com/questions/56583395/how-can-i-combine-ember-bootstrap-and-ember-autoresize/56583948

components.bs-form.element.control.textarea.js

import BootstrapTextareaComponent from 'ember-bootstrap/components/bs-form/element/control/textarea';
import AutoResizeMixin from 'ember-autoresize/mixins/autoresize';
import { computed, get } from '@ember/object';
import { isEmpty, isNone } from '@ember/utils';	

export default BootstrapTextareaComponent.extend(AutoResizeMixin, {
  autoresize: true,
  shouldResizeHeight: true,
  significantWhitespace: true,
  autoResizeText: computed('value', 'placeholder', {
    get() {
      var placeholder = get(this, 'placeholder');
      var value = get(this, 'value');
      var fillChar = '@';

      if (isEmpty(value)) {
        return isEmpty(placeholder) ? fillChar : placeholder + fillChar;
      }

      if (isNone(value)) {
        value = '';
      }

      return value + fillChar;
    }
  })
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: "Ember\nTwiddle",
});

templates.application.hbs

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


{{#bs-form model=this formLayout="vertical" as |form|}}
  {{form.element label="Inline" placeholder="Enter description..." property="appName" controlType="textarea"}}
{{/bs-form}}

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-bootstrap": "2.8.0",
    "ember-autoresize": "1.3.2"
  }
}