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Optional Features


One of the ways that Ember releases guarantee stability is by following Semantic Versioning (SemVer). For the Ember project this means that any feature that is to be removed must first be deprecated, and only removed when a major version is released. It also means that new features are introduced in a backwards compatible way.

To give the project a path forward when a breaking change is mandatory, we've released the @ember/optional-features addon.

This addon does nothing by default, but provides a command-line interface to enable and disable breaking changes in Ember.

Installation

To get started with optional features, you must install the addon:

ember install @ember/optional-features

This will make three new commands available to Ember CLI within your project, feature:list, feature:enable, and feature:disable.

Listing features

The optional features available to your project will depend on the Ember version your project is using.

To see which optional features are available, you can run the following command:

$ ember feature:list
Usage:

  To list all available features, run ember feature:list.
  To enable a feature, run ember feature:enable some-feature.
  To disable a feature, run ember feature:disable some-feature.

Available features:

  application-template-wrapper (Default: true)
    Wrap the top-level application template (application.hbs) with a `<div class="ember-view">` element.
    More information: https://github.com/emberjs/rfcs/pull/280

  jquery-integration (Default: true)
    Adds jQuery to the Ember application.
    More information: https://github.com/emberjs/rfcs/pull/294

Features

Once you see a feature that you would like to toggle for your project you can run one of two commands, ember feature:enable <feature> and ember feature:disable <feature>.

Let us disable jquery-integration to see what happens:

$ ember feature:disable jquery-integration
Disabled jquery-integration. Be sure to commit config/optional-features.json to source control!

As we can see from the warning, @ember/optional-features has created a file in config/optional-features.json to store the configuration for your project. We commit it to our repository and we are off to the races!

jquery-integration

jQuery is commonly used for event handling and many popular libraries for charting and UI components. With the release of Octane, Ember does not include jQuery by default. However, you may choose to install and use it in your app!

Including jQuery

To include jQuery in your Ember app, follow the instructions above to install @ember/optional-features. Next, enable the feature:

ember feature:enable jquery-integration

Then, install the @ember/jquery addon:

ember install @ember/jquery

Now, almost anywhere in your app, you can use this.$() to use jQuery methods.

Removing jQuery

If you are working on an application that already has jQuery installed, and would like to remove it, follow these steps.

First, refactor your own code to not depend on jQuery. Keep in mind that if any of your app's dependencies use jQuery, you will need to find an alternative for them.

Next, follow the instructions above to install @ember/optional-features, and run the following command to change @ember/optional-features:

ember feature:disable jquery-integration

Then, remove @ember/jquery from your package.json.

This will remove jQuery from your vendor.js bundle and disable any use of jQuery in Ember itself. Now your app will be about 30KB lighter!

Caveats

Without jQuery, any code that still relies on it will break, especially the following usages:

  • this.$() in components
  • jQuery or $ directly as a global, through Ember.$() or by importing it (import jQuery from jquery;)
  • global acceptance test helpers like find() or click()
  • this.$() in component tests

Note that this also applies to all addons that your app uses, so make sure they support being used without jQuery.

application-template-wrapper

With this feature enabled Ember creates a wrapping div around the entire rendered application. Effectively, it is creating a <div class="ember-view"> element which wraps the contents of an application's app/templates/application.hbs file.

When disabled, this div will not be output. This is usually desirable, but may break the styling of an existing application in subtle ways:

  • Perhaps the application relied on the root .ember-view for styles (CSS).
  • Perhaps the <div> itself was the target of styles (e.g. body > div > .some-child).
  • The presence of a wrapping <div> means the application is contained in a block-layout element. When removed, and depending on if the application specifies a rootElement in config/environment.js, the application may no longer be contained in a block-layout element.

If your application relies on those behaviors it is still recommended that you disable this feature, and simply add an appropriate element to app/templates/application.hbs wrapping that template's {{outlet}}.

For more information, see RFC #280.

template-only-glimmer-components

With this feature disabled Ember will create an implicit element for components which have no JavaScript file ("template-only components").

Enabling this feature will result in only the contents of the template being rendered, and additionally in no classic Ember component instance being instantiated to provide it context.

Some examples of how enabling this feature impacts app code are:

  • In template-only component templates statements like {{this}}, {{this.foo}} and {{foo}} will be undefined. Accessing arguments as {{@foo}} will continue to work.
  • If this feature is enabled in an application with existing template-only components, the removal of the wrapping <div> will happen to all uses of those template-only components. This can impact style and logic in a breaking manner.
  • Passing classes to an invocation (i.e. {{my-component class="..."}}) will no longer result in those classes being present on any element. This could be a change in behavior which impacts any reflected attribute passed as an argument, such as id= or tagName=.
  • Templates can use ...attributes to target attributes and element modifiers passed from an angle bracket invocation.

Enabling this feature makes template-only components more consistent with angle-bracket invocation and with Glimmer components. Additionally it improves the performance of template-only components (there is no JS object instantiated to provide context) and makes them an excellent replacement for use of Ember's more complex and now discouraged API {{partial.

It is recommended that you enable this feature. Existing applications adopting this optional feature should add a .js file for any existing template-only components containing a basic Ember component class. This will maintain backwards compatibility for existing templates while new template-only components gain the advantages of this feature.

For more information, see RFC #278.

default-async-observers

With this feature enabled, Ember will run all observers in the application asynchronously by default. This leads to observers running in the run loop after the one in which the observed properties were updated.

If the feature is disabled, observers run synchronously and will be invoked as soon as their observed properties update.

Async observers are more performant than those that run synchronously and can help you to manage your application state in a more predictable manner. This is one of the reasons, why the default-async-observers feature is enabled by default in newly created, modern Ember applications.

The default-async-observers feature affects the behavior of observers application-wide, but you can still instruct individual observers to run synchronously or async manually. By using the sync: true option, observers who are otherwise async by default can be marked as synchronous manually. Similarly, observers can be set to run asynchronously using the sync: false option.

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

Person.extend({
  partOfNameChanged: observer({
    dependentKeys: ['firstName', 'lastName'],
    fn() {
      // Fires async after firstName or lastName have updated
    },
    sync: false,
  })
});

While the default-async-observers feature is only enabled by default in modern Ember applications, you can enable this optional feature in older apps (Ember 3.13+) as follows:

$ ember feature:enable default-async-observers
# Enable async observers application-wide. Be sure to commit config/optional-features.json to source control!