access property inside computed

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: "ember-twiddle",
  allItems: ['a', 'b'],
  sortedItems: Ember.computed.sort('allItems', function(a, b) {
    alert(this.get('columnList'));
  }),
  columnList: ["name","shortcode"],
  init() {
    this.get('sortedItems');  
  }
});

templates.application.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.15.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.js",
    "ember": "3.4.3",
    "ember-template-compiler": "3.4.3",
    "ember-testing": "3.4.3"
  },
  "addons": {
    "ember-data": "3.4.2"
  }
}