Deprecation Guide for Use defineProperty to define computed properties

Although uncommon, it is possible to assign computed properties directly to objects and have them be implicitly computed from eg Ember.get. As part of supporting ES5 getter computed properties, assigning computed properties directly is deprecated. You should replace these assignments with calls to defineProperty.

For example, the following:

let object = {};
object.key = Ember.computed(() => 'value');
Ember.get(object, 'key') === 'value';

Should be changed to:

let object = {};
Ember.defineProperty(object, 'key', Ember.computed(() => 'value'));
Ember.get(object, 'key') === 'value';