New Twiddle

controllers.application\.js

import Controller from '@ember/controller';

import { computed, set } from '@ember/object';

export class Room {

    _localAttributes = {};
    _remoteAttributes = {};

    save() {
        this._remoteAttributes.capacity = this._localAttributes.capacity
        delete this._localAttributes.capacity;
        // set(this._localAttributes, 'capacity', undefined);
    }

    @computed('_localAttributes.capacity', '_remoteAttributes.capacity')
    get capacity() {
        return this._localAttributes.capacity !== undefined
        ? this._localAttributes.capacity
        : this._remoteAttributes.capacity !== undefined
            ? this._remoteAttributes.capacity : null;

    }
    set capacity(value) {
        const newValue = value !== null ? value : null;
        set(this._localAttributes, 'capacity', newValue);
        if (this._localAttributes.capacity !== newValue) {
            throw Error('Failed to set key');
        }
        return value;
    }

}

export default class ApplicationController extends Controller {
  appName = 'Ember Twiddle';

  init() {
    super.init(...arguments);
    const room = new Room();
    room.capacity = 1
    console.log(room.capacity);
    room.save();
    console.log(room.capacity);

    room.capacity = 2; // Error thrown here when setting room.capacity
    console.log(room.capacity);  }
}

templates.application\.hbs

<h1>Welcome to {{this.appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle\.json

{
  "version": "0.17.1",
  "EmberENV": {
    "FEATURES": {},
    "_TEMPLATE_ONLY_GLIMMER_COMPONENTS": false,
    "_APPLICATION_TEMPLATE_WRAPPER": true,
    "_JQUERY_INTEGRATION": true
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.js",
    "ember": "3.18.1",
    "ember-template-compiler": "3.18.1",
    "ember-testing": "3.18.1"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}