state

controllers.application\.js

import Controller from '@ember/controller';

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

helpers.not\.js

import { helper } from '@ember/component/helper';

export default helper(([v]) => !v);

helpers.state-from\.js

import { helper } from '@ember/component/helper';
import { tracked } from '@glimmer/tracking';

class State {
  @tracked value;

  constructor(value) {
    this.value = value;
  }
  
  update = (newValue) => (this.value = newValue);
}

export default helper(([initial]) => new State(initial));

templates.application\.hbs

{{#let (state-from false) as |state|}}
  <p>state: {{if state.value "yep" "nope"}}</p>
  <button {{on "click" (fn state.update (not state.value))}}>flip it</button>
{{/let}}

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"
  }
}