glimmer

components.show-item.js

import Ember from 'ember';

export default Ember.Component.extend({
  tagName: 'li',
});

controllers.application.js

import Ember from 'ember';


export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  items: Ember.A(['Item 1', 'Item 2', 'Item 3', 'Item 4']),
  
  actions: {
    
    moveDown(index) {
      
      var items = this.get('items');
      var item = items.objectAt(index);
      var before = items.slice(0,index);
      var after = items.slice(index + 1 );
      items = before.concat(after);
      before = items.slice(0,index + 1);
      after = items.slice(index + 1);
      before.push(item);
      this.set('items', before.concat(after) );
      
    }
  }
});

templates.application.hbs

<ul>
{{#each items as |item index|}}

  {{show-item item=item onMoveDown=(action 'moveDown' index)}}

{{/each}}
</ul>
{{outlet}}

templates.components.show-item.hbs

{{item}}<button onclick={{action onMoveDown}}>▼</button>

twiddle.json

{
  "version": "0.15.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.2.2",
    "ember-template-compiler": "3.2.2",
    "ember-testing": "3.2.2"
  },
  "addons": {
    "ember-data": "3.2.0"
  }
}