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Disabling Prototype Extensions

By default, Ember.js will extend the prototypes of native JavaScript objects in the following ways:

  • Array is extended to implement the Ember.Enumerable, Ember.MutableEnumerable, Ember.MutableArray and Ember.Array interfaces. This polyfills ECMAScript 5 array methods in browsers that do not implement them, adds convenience methods and properties to built-in arrays, and makes array mutations observable.
  • String is extended to add convenience methods, such as camelize() and fmt().
  • Function is extended with methods to annotate functions as computed properties, via the property() method, and as observers, via the observes() or observesBefore() methods.

This is the extent to which Ember.js enhances native prototypes. We have carefully weighed the tradeoffs involved with changing these prototypes, and recommend that most Ember.js developers use them. These extensions significantly reduce the amount of boilerplate code that must be typed.

However, we understand that there are cases where your Ember.js application may be embedded in an environment beyond your control. The most common scenarios are when authoring third-party JavaScript that is embedded directly in other pages, or when transitioning an application piecemeal to a more modern Ember.js architecture.

In those cases, where you can't or don't want to modify native prototypes, Ember.js allows you to completely disable the extensions described above.

To do so, simply set the EXTEND_PROTOTYPES flag to false:

window.EmberENV = {};

Or you can choose class which you want to disable prototype extension.

  String: false,
  Array: true

Note that the above code must be evaluated before Ember.js loads. If you set the flag after the Ember.js JavaScript file has been evaluated, the native prototypes will already have been modified.

Life Without Prototype Extension

In order for your application to behave correctly, you will need to manually extend or create the objects that the native objects were creating before.


Native arrays will no longer implement the functionality needed to observe them. If you disable prototype extension and attempt to use native arrays with things like a template's {{#each}} helper, Ember.js will have no way to detect changes to the array and the template will not update as the underlying array changes.

Additionally, if you try to set the model of an Ember.ArrayController to a plain native array, it will raise an exception since it no longer implements the Ember.Array interface.

You can manually coerce a native array into an array that implements the required interfaces using the convenience method Ember.A:

var islands = ['Oahu', 'Kauai'];
//=> TypeError: Object Oahu,Kauai has no method 'contains'

// Convert `islands` to an array that implements the
// Ember enumerable and array interfaces

//=> true


Strings will no longer have the convenience methods described in the Ember.String API reference.. Instead, you can use the similarly-named methods of the Ember.String object and pass the string to use as the first parameter:

//=> TypeError: Object my_cool_class has no method 'camelize'

//=> "myCoolClass"


To annotate computed properties, use the Ember.computed() method to wrap the function:

// This won't work:
fullName: function() {
  return this.get('firstName') + ' ' + this.get('lastName');
}.property('firstName', 'lastName')

// Instead, do this:
fullName: Ember.computed('firstName', 'lastName', function() {
  return this.get('firstName') + ' ' + this.get('lastName');

Observers are annotated using Ember.observer():

// This won't work:
fullNameDidChange: function() {
  console.log("Full name changed");

// Instead, do this:
fullNameDidChange: Ember.observer('fullName', function() {
  console.log("Full name changed");