Ember.js getters/setters

controllers.application\.js

import Controller from '@ember/controller';
import { action } from '@ember/object';
import { tracked } from '@glimmer/tracking';

const DEFAULT_A = [ 'default_a' ];
const DEFAULT_B = [ 'default_b' ];

export default class AppController extends Controller {
  @tracked _prop_A = DEFAULT_A.slice();
  @tracked _prop_B = DEFAULT_B.slice();

  get prop_A() {
    return this._prop_A;
  }
  set prop_A(value) {
    this._prop_A = value;
  }

  get prop_B() {
    return this._prop_B;
  }
  set prop_B(value) {
    if (value === undefined) {
      this._prop_B = DEFAULT_B.slice();
    } else {
    	this._prop_B = [ `new value b${value}` ];
    	this.prop_A = [ ...this.prop_A, value ];
    }
  }

  @action update_A(shouldAdd) {
    const arr = this.prop_A.slice();
    
    if (shouldAdd === true) {
      this.prop_A = [ ...arr, arr.length ];
    } else if (shouldAdd === false) {
      this.prop_A = arr.slice(0, -1);
    } else {
      this.prop_A = DEFAULT_A.slice();
    }
  }

  @action update_B(value) {
    this.prop_B = value;
  }
}

templates.application\.hbs

<button {{on "click" (fn this.update_A true)}}>
  Add to `prop_A`
</button>

<button {{on "click" (fn this.update_A false)}}>
  Remove from `prop_A`
</button>

<button {{on "click" (fn this.update_A undefined)}}>
  Reset `prop_A`
</button>

<br>
<br>

<button {{on "click" (fn this.update_B 1)}}>
  Set `prop_B` with 1
</button>

<button {{on "click" (fn this.update_B 2)}}>
  Set `prop_B` with 2
</button>

<button {{on "click" (fn this.update_B undefined)}}>
  Reset `prop_B`
</button>

<hr>

this.prop_A => {{this.prop_A}}

<br>
<br>

this.prop_B => {{this.prop_B}}

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",
    "@glimmer/tracking": "1.0.0"
  },
  "addons": {
    "@glimmer/component": "1.0.0"
  }
}