avoid-leaking-state-in-components

components.test-component-with-init.js

import Ember from 'ember';

export default Ember.Component.extend({
  init() {
    this._super(...arguments);
    this.set('items', [
      'this is a default value',
      'it shouldn’t appear if `items` is passed in from the parent'
    ]);
  }
});

components.test-component.js

import Ember from 'ember';

export default Ember.Component.extend({
  items: [
    'this is a default value',
    'it shouldn’t appear if `items` is passed in from the parent'
  ]
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  
  someItems: [
  	'these are values',
    'that are passed in from the controller'
  ]
});

templates.application.hbs

{{test-component items=someItems}}

{{test-component-with-init items=someItems}}

templates.components.test-component-with-init.hbs

<ul>
  {{#each items as |item|}}
    <li>{{item}}</li>
  {{/each}}
</ul>

templates.components.test-component.hbs

<ul>
  {{#each items as |item|}}
    <li>{{item}}</li>
  {{/each}}
</ul>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}