Staggered Record Loading

adapters.application.js

import Ember from 'ember';
import RSVP from 'rsvp';

export default Ember.Object.extend({
  findRecord(_, __, id) {
    return new RSVP.Promise(resolve => {
      setTimeout(resolve, parseInt(id) * 350);
    }).then(() => {
      return {
        data: {
          type: 'user',
          id,
          attributes: {
            name: 'user-' + id
          }
        }
      };
    });
  },
  query() {
    return RSVP.resolve({
      data: [
        { type: 'user', id: '1' },
        { type: 'user', id: '2' },
        { type: 'user', id: '3' },
        { type: 'user', id: '4' },
        { type: 'user', id: '5' },
        { type: 'user', id: '6' }
      ]
    });
  }
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({});

models.user.js

import Model from 'ember-data/model';
import attr from 'ember-data/attr';
import { belongsTo, hasMany } from 'ember-data/relationships';

export default Model.extend({
  name: attr()
});

routes.application.js

import Ember from 'ember';

const LazyList = Ember.ArrayProxy.extend({
  setContent(content) {
    this._loaded = new Set();
    this.set('content', content);
  },
  objectAt(index) {
    const record = this.content.objectAt(index);
    const { type } = this;
    const { id } = record;
    const reload = !this._loaded.has(record.id);
    if (reload) {
      this._loaded.add(record.id)
    }
    return this.store.findRecord(type, id, { reload });
  }
});

export default Ember.Route.extend({
  init() {
    this._super(...arguments);
    this.list = LazyList.create({ type: 'user', store: this.store });
  },
  model() {
  	return this.store.query('user', {})
      .then(recordArray => {
         this.list.setContent(recordArray);
         return this.list;
       });
  }
});

serializers.application.js

import Ember from 'ember';

export default Ember.Object.extend({
  normalizeResponse(_, __, data) { return data; }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
<ol>
{{#each model as |user|}}
  <li>{{user.name}}</li>
{{/each}}
</ol>
<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"
  }
}