ember-property-initializers.js

import EmberObject from '@ember/object';

class SubclassWithEmberInit extends EmberObject {
  someProp = 'value';
  
  init() {
    super.init(...arguments);
    console.log(this.someProp); // undefined
    // `this.someProp` will be available after initialization,
    // just not from the `init` method...
  }
}

class SubclassWithConstructor extends EmberObject {
  someProp = 'value';
  
  constructor() {
    super(...arguments);
    console.log(this.someProp); // "value"
  }
}