vert?

controllers.application.js

import Ember from 'ember';

function createArrayWithLength(n) {
  var arr = [], i;
  for(i = 0; i < n; i++) {
    arr.push(i);
  }
  return arr;
}

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items: createArrayWithLength(100) 
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{#vertical-collection
    items
    tagName='ul'
    estimateHeight=50
    staticHeight=false
    bufferSize=1
    renderAll=false
    renderFromLast=false
    idForFirstItem=idForFirstItem
    firstReached=firstReached
    lastReached=lastReached
    firstVisibleChanged=firstVisibleChanged
    lastVisibleChanged=lastVisibleChanged
     as |item i|}}
    <li>
      {{item.number}} {{i}}
    </li>
{{/vertical-collection}}
<br>
<br>

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-data": "3.4.2",
    "@html-next/vertical-collection": "1.0.0-beta.12"
  }
}