Using Object.defineProperty with Angular throws TypeError: Cannot assign to read only property (property) of #<Object>

Question

I have an object on my scope, and I want that object to have a few non-enumerable properties, but after setting the enumerable descriptor to false, whenever I try to change the value, I get: "TypeError: Cannot assign to read only property (property) of #"

... even though I am specifically setting it's writeable and configurable descriptors to true. Why is this happening, and what can I do to fix it? In non-strict mode it doesn't throw an error, it just doesn't do anything. This should work fine according to: MDN ...

code:

'use strict'
angular.module('app', []);

angular.module('app').controller('TestingCtrl',['$scope', function($scope){
  var that = this;  
  this.content = { contentArea: {} };
  
  function updateIsEmpty(){
    that.content.contentArea.isEmpty = Object.keys(that.content.contentArea).length === 0;
    console.log(that.content.contentArea)
    console.log(Object.keys(that.content.contentArea));
  }
  
  this.addSomethingToCA = function(val){
    that.content.contentArea.something = val;
    updateIsEmpty();
  };
  this.removeSomethingFromCA = function(){
    delete that.content.contentArea.something;
    updateIsEmpty();
  };
  
  (function init(){
    Object.defineProperty(that.content.contentArea, 'isEmpty', {
      enumerable: false
    , value: true
    , configurable: true
    , writeable: true
    });
   
  })();
}]);

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js"></script>
<div ng-app="app">
  <div ng-controller="TestingCtrl as testingctrl">
    <button ng-if="testingctrl.content.contentArea.isEmpty === true" 
            ng-click="testingctrl.addSomethingToCA('is weird')">add something</button>
    
    <button ng-click="testingctrl.removeSomethingFromCA()">remove something</button>
    <ul>
      <li ng-repeat="(key, val) in testingctrl.content.contentArea">
        key: {{ key }} 
        val: {{ val }}
      </li>
    </ul>
  </div>
</div>

if you run the above code snippet it throws: TypeError:

 Cannot assign to read only property 'isEmpty' of #<Object>
    at updateIsEmpty (http://stacksnippets.net/js:35:38)
    at removeSomethingFromCA (http://stacksnippets.net/js:46:5)
    at https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:161:190
    at https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:178:83
    at h.$eval (https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:101:273)
    at h.$apply (https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:102:48)
    at HTMLButtonElement.<anonymous> (https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:178:65)
    at https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:27:15
    at Array.forEach (native)
    at q (https://ajax.googleapis.com/ajax/libs/angularjs/1.2.4/angular.min.js:7:255)

Answer 1

You have a typo. Your writeable key in the property descriptor should be writable.