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 w(). You can find a list of these methods with the Ember.String documentation.

  • Function is extended with methods to annotate functions as computed properties, via the property() method, and as observers, via the observes() method. Use of these methods is now discouraged and not covered in recent versions of the Guides.

This is the extent to which Ember.js enhances native prototypes. We have carefully weighed the trade-offs 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 EmberENV.EXTEND_PROTOTYPES flag to false:

ENV = {
  EmberENV: {
    EXTEND_PROTOTYPES: false
  }
}

You can configure which classes to include prototype extensions for in your application's configuration like so:

ENV = {
  EmberENV: {
    EXTEND_PROTOTYPES: {
      String: false,
      Array: true
    }
  }
}

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.

Arrays

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.

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

import { A } from '@ember/array';

let islands = ['Oahu', 'Kauai'];
islands.includes('Oahu');
// => TypeError: Object Oahu,Kauai has no method 'includes'

// Convert `islands` to an array that implements the
// Ember enumerable and array interfaces
A(islands);

islands.includes('Oahu');
// => true

Strings

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:

import { camelize } from '@ember/string';

'my_cool_class'.camelize();
// => TypeError: Object my_cool_class has no method 'camelize'

camelize('my_cool_class');
// => "myCoolClass"

Functions

The Object Model section of the Guides describes how to write computed properties, observers, and bindings without prototype extensions. Below you can learn about how to convert existing code to the format now encouraged.

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

import { computed } from '@ember/object';

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


// Instead, do this:
fullName: computed('firstName', 'lastName', function() {
  return `${this.get('firstName')} ${this.get('lastName')}`;
})

Observers are annotated using Ember.observer():

import { observer } from '@ember/object';

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


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

Evented functions are annotated using Ember.on():

import { on } from '@ember/object/evented';

// This won't work:
doStuffWhenInserted: function() {
  /* awesome sauce */
}.on('didInsertElement');

// Instead, do this:
doStuffWhenInserted: on('didInsertElement', function() {
  /* awesome sauce */
});

© 2020 Yehuda Katz, Tom Dale and Ember.js contributors
Licensed under the MIT License.
https://guides.emberjs.com/v2.18.0/configuring-ember/disabling-prototype-extensions