By default, Ember.js will extend the prototypes of native JavaScript objects in the following ways:
Array
is extended to implement theEmber.Enumerable
,Ember.MutableEnumerable
,Ember.MutableArray
andEmber.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 ascamelize()
andw()
. 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 theproperty()
method, and as observers, via theobserves()
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 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 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.
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
:
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
Ember.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:
"my_cool_class".camelize();
//=> TypeError: Object my_cool_class has no method 'camelize'
Ember.String.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:
// 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');
}.observes('fullName')
// Instead, do this:
fullNameDidChange: Ember.observer('fullName', function() {
console.log('Full name changed');
})
Evented functions are annotated using Ember.on()
:
// This won't work:
doStuffWhenInserted: function() {
/* awesome sauce */
}.on('didInsertElement');
// Instead, do this:
doStuffWhenInserted: Ember.on('didInsertElement', function() {
/* awesome sauce */
});