arrays are dumb

controllers.application\.js

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

const PREFILL_DATA = [{name: 'bill'}, {name: 'aubrey'}, {name: 'danston'}];

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

  _nameArray = A(PREFILL_DATA);
	numberSelected = this._nameArray.length;

	@computed('numberSelected', '_nameArray.[]')
  get nameArray() {
    const diff = this.numberSelected - this._nameArray.length;
    if (diff > 0) {
      console.log('longer', diff);
      for (let i = 0; i < diff; i++) {
        this._nameArray.push({name: ''});
      }
    } else if (diff < 0) {
      const shorter = this._nameArray.slice(0, this.numberSelected);
      this.set('_nameArray', shorter);
    }
    return this._nameArray;
  }

	@action
  selected(event) {
    this.set('numberSelected', Number.parseInt(event.target.value, 10));
  }

	@action
	updateName(index, event) {
    console.log(this._nameArray);
    this.set(`_nameArray.${index}.name`, event.target.value);
  }
}

templates.application\.hbs

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

<p>{{this.numberSelected}}</p>
<select onchange={{action selected}}>
  <option value=1>1</option>
  <option value=2>2</option>
  <option value=3>3</option>
  <option value=4>4</option>
  <option value=5>5</option>
</select>
<br><br><br>

<p>length: {{this.nameArray.length}}</p>

{{#each this.nameArray as |name index|}}
	{{name.name}}
  {{index}}
	<input value={{name.name}} {{on "input" (fn updateName index)}} />
  <br>
{{/each}}
<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"
  }
}