Today the Ember project is releasing version 4.0 of Ember.js, Ember Data, and
Ember CLI. Ember's 4.0 release focuses
the framework by removing long-deprecated APIs and support for legacy platforms.
This blog post will help you understand how to upgrade and navigate any breaking
changes.
Although Ember "Octane" APIs have been
the default for new applications since Ember 3.15, the framework has continued
to support "Classic" framework features in accordance with our semantic
versioning commitment. Ember 4.0 takes a step forward and drops
already-deprecated classic APIs, however the foundational EmberComponent and
EmberObject/computed APIs are not removed in this release.
Additionally, today we're promoting Ember 3.28 to become Ember's latest
Long-Term Support (LTS) release. Ember's LTS release process provides bugfix
support for about 36 weeks, and security patches for about 54 weeks. See the
3.28 release post and LTS
documentation for more details.
For applications using LTS releases, upgrading directly to 4.0 is not
encouraged. Best practice for those applications is to upgrade to Ember 3.28 LTS
as soon as possible, then wait for the first LTS of the 4.0 series to be
released. Ember 4.4 will be the first candidate.
Major Releases in Ember
Starting with Ember 2.0, major versions of Ember have been about removal
of deprecated APIs, and not about the introduction of new features or development styles.
Ember 4.0 follows that tradition, and will contain no new features.
Our plans for Ember 4.0 were originally announced in July 2021 in
The Road to Ember 4.0.
Trying Ember for the first time
If you're interested in trying Ember for the
first time today, get started by running:
# Make sure you are on the latest npm version, 8.x
npm --version
npx ember-cli@latest new my-project
cd my-project
npm start
# Then visit http://localhost:4200

How to upgrade your project to Ember 4
If your app or addon runs with no deprecations in the latest release of 3.28
you should be able to upgrade to Ember 4 with no additional changes. Depending
on how up to date your dependencies are, you may want to upgrade several of
those before the jump including ember-data, ember-auto-import, and
ember-cli-htmlbars
Follow these steps in order:

1. Upgrade your project to the latest patch version of Ember 3.28.
   Many developers can do this by running
   npx ember-cli-update --to 3.28. The
   general Ember upgrade guide
   has more details about how to upgrade your Ember app/addon.
2. Upgrade the ember-cli-htmlbars dependency (if present) to the latest patch
   release of 6.x. The final patch releases of the 5.x and 6.x series
   include important fixes for how deprecations are presented.
3. Install ember-auto-import. If your app does not already have it as a
   dependency, follow the ember-auto-import installation
   documentation. The
   short version is: npm i --save-dev ember-auto-import webpack.
   If you are already using ember-auto-import, make sure you are using release
   2.x or better.
   You can follow
   this upgrade guide
   if you are on an earlier version.
4. Make sure your app builds successfully.
5. Resolve all deprecation warnings. Deprecated APIs are removed in Ember 4.0. You
   may need to upgrade some of your dependencies if they are using deprecated
   APIs. See the Ember Deprecation Guide
   for more details about specific deprecations and how to resolve them.
   Applications that need to upgrade through several versions may want to
   consider isolating individual deprecations by using
   ember-cli-deprecation-workflow.
6. Make sure your app builds successfully and your test suite passes with no
   deprecations.
7. Upgrade your app to Ember 4.0. Again,
   many developers can do this by running
   npx ember-cli-update --to 4.0. Refer to the
   general Ember upgrade guide
   for more details about how to upgrade your Ember app/addon.

Notable changes
Browser Support in Ember 4
Ember 4.0 supports two classes of browsers: Evergreen (those on a weeks-long, auto-upgrade release cycle) and non-evergreen. This classification system allows us to create a rolling minimum version for evergreen browsers, while using a more traditional, pinned minimum version for non-evergreen browsers.
Specifically, the Ember 4.x release policy includes support for Google Chrome, Mozilla Firefox, Microsoft Edge, and Apple Safari on desktop and mobile. It does not include support for any version of Internet Explorer.
Supported browser ranges:

• Chrome >= 92
• Edge >= 93
• Firefox >= 91
• iOS >= 12
• Safari >= 12
• Chrome Android >= 96
• Firefox Android >= 94

Read more about this change in the deprecation guide and at Ember's browser support policy page.
ember-auto-import is a required dependency
Using Ember 4.x requires that your project depends on version 2.0+
of the ember-auto-import addon.
Follow the "How to upgrade" steps above to learn how to upgrade.
Why is this dependency required? ember-auto-import implements support in
Ember CLI for something we call the
v2 addon
format.
This specification describes how to publish an Ember CLI addon that has minimal
build overhead and better compatibility with modern build and analysis tooling
(ala Webpack). Later in Ember's 4.x release cycle,
we intend to release framework libraries as v2 addons to take advantage of those
improvements. Mandating the library is installed for 4.0 prepares Ember projects
for that eventual change.
Changes in Ember.js 4.0
Ember.js is the core of the Ember framework. It provides routing, rendering, and
dependency injection features.
Ember.js 4.0 introduces no new public API. Instead, it is comprised of bug fixes
and the removal of previously deprecated public API from the 3.x cycle.
Ember 4.0 does not remove the EmberComponent API or the core parts of the
EmberObject system. These APIs are widely used, even after the release of
Octane, by existing application and addon code.
APIs Removed in 4.0
Below we've listed some of the most significant API removals in Ember.js 4.0.
For a complete list of removals, see the Ember.js 3.x deprecation
guide.

• Ember.Logger is removed in favor of native console APIs. Guide here.
• Copyable mixin is removed in favor of the ember-copy addon. Guide here.
• sendAction is removed in favor of calling closure actions like any other callback. Guide here.
• willTransition and didTransition are removed in favor of router service events. Guide here.
• Computed Property volatile() calls are removed in favor of native getters. Guide here.
• this.$() and other jQuery APIs have been removed in favor of native browser equivalents. Guide here. An optional feature which restored jQuery-specific features is also removed. Guide here.
• {{partial}} is removed in favor of template-only components. Guide here.
• Using the built-in global resolver (App.FooController anyone?) is deprecated in favor of using ember-resolver, already the default for Ember CLI generated apps. Guide here.
• Ambiguous references to a component's properties are removed. You must now write {{this.someProp}}. Guide here.
• renderTemplate is removed in favor of {{in-element}} or other rendering target redirection like ember-wormhole. Guide here.
• Support for the Ember global on window is removed in favor of importing the Ember object or using the module-based API. Guide here.
• Support for certain features of the , , and components are removed. See guides on positional arguments, legacy arguments, legacy HTML attributes, and importing legacy built-in components.
• The internal APIs of , , , and are now private,
  and subclassing them is no longer supported.
  An example of subclassing looks like this: export class MyLinkComponent extends LinkTo.
  Apps or addons that subclass can install
  the library @ember/legacy-built-in-components
  as a stepping stone, following this deprecation guide.
• …and additional uncommon deprecations found in the Ember.js 3.x deprecation
  guide

Many of these removed APIs date back to Ember 1.x, and are rarely used now (or should be rarely used).
For more details on the changes in Ember.js 4.0, please review the
Ember.js 4.0.0 release page.
Deprecations added in 4.0
The following public API, marked as deprecated in Ember 4.0, will be removed in
Ember 5.0:

• Use of Ember.assign is deprecated. You should replace any calls to Ember.assign with Object.assign or use the object spread operator. See the deprecation guide for examples.

Changes in Ember Data 4.0
Ember Data is the official data persistence library for Ember.js applications.
This release removes APIs that were deprecated in the 3.x cycle. Examples include:

• The API store.defaultAdapter is removed - deprecation guide
• Support for relying on fallback behavior for adapter type is removed.
  You should specify adapter types explicitly.
• Similarly, adapter.defaultSerializer and support for relying on fallback behavior for the
  serializer type is removed
• The Evented API is removed
• …and other APIs listed in the deprecation guide

For more details on the changes in Ember Data 4.0, please review the
Ember Data 4.0.0 release page.
Changes in Ember CLI 4.0
Ember CLI is the command line interface for managing and packaging Ember.js
applications.
Some notable changes in Ember CLI 4.0 include:

• When generating a new Ember app (ember new appname) or addon
  (ember addon addonname) the option --ci-provider is now available. This
  can be passed travis or github to generate the appropriate CI
  configuration files. See
  ember-cli/ember-cli#9579
  for more details.
• Additionally, the default CI provider for newly generated apps and addons
  is now GitHub Actions (replacing TravisCI).
• Ember CLI's EmberApp accepts an option addons to manually control which
  installed addons will be run during the build. The properties exclude
  and include on this option have been introduced to replace the properties
  blacklist and whitelist. The replaced properties will continue to function
  until they can undergo a full deprecation and major release cycle. This
  change is in support of RFC
  639.

For more details on the changes in Ember CLI 4.0 and detailed upgrade
instructions, please review the Ember CLI 4.0.0 release page.
Need help?
Are you stuck on something? Do you have questions?
Visit one of our community chat groups.
What next?
Want to help make Ember 4 a success? Here are some things you can do!

• Blog about your experience.
• If someone helps you with a question, consider posting both the question
  and answer to a public place like Stack Overflow or the Ember Discourse forums,
  so that others can learn from it.
• Help your favorite addons to upgrade to Ember 4!
• Stay tuned via the Ember Times for new features and requests for help
  implementing them.

Thank You!
We want to offer a heart-felt "thank you" to our the amazing Ember 4.0
contributors. This
release was a wide-ranging effort with over 50 API removals in
the ember-source package alone, and required coordination of timelines and
execution across all Ember's core libraries and teams. Ember is a project
maintained largely by volunteers, and this release is the result of sustained
contribution across many codebases, timezones, and interests.
We deeply appreciate the support of our contributors and user community. Thank
you.