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Embroider: translating existing Ember code into spec-compliant modern JavaScript

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This repo implements a new three-stage build system for Ember apps:

  1. The first stage achieves backward compatibility by building each classic Ember Addon package into a new v2 package format. This makes each package much more static and analyzable. The eventual goal is to do less and less work in this stage, as addons publish to NPM natively in v2 format.

  2. The second stage takes a collection of v2-formatted addons plus an application and "compiles out" all Ember-specific conventions, such that the output can be understood by any tool that can handle standards-compliant Javascript. This stage is setup with good inputs and outputs that make it much easier to benefit from incremental improvements to our dependency analysis. The immediate goal is not to implement every possible optimization, but rather to make a good place for those optimizations to happen.

  3. The third stage ("final packaging") can be handled by existing tools like Webpack, Rollup, or Parcel with only a small amount of configuration. Not because we want to force every Ember developer to choose and configure one of these tools! But because a stable, standards-compliant API between stage 2 and 3 improves our ability to innovate and experiment with taking the best parts of wider JS ecosystem tooling.

You can read more about the motivation and key ideas in the intro to the SPEC.

Status / Should I Use It?

Several large, heavily-tested Ember apps are shipping to production with Embroider. So if you are excited to adopt Embroider, it is a reasonable choice. The main risks to be aware of if you choose to use Embroider in production are:

  • you're likely to discover some Ember addons don't work or break your build
  • Embroider's own configuration options are subject to change, so you'll need to read the when updating the Embroider packages.

Alternatively, it is totally safe to stick with the traditional build pipeline and wait for the official cutover point when EmberCLI starts generating new apps with Embroider by default.

For Addon Authors

Addon authors should see for advice on how to get their existig addons ready for Embroider.

The v2 Addon Format RFC is the official spec for the packages that Embroider natively handles. Common patterns and best practices for authoring these have been collected in the v2 addon FAQs. For creating a new v2 addon from scratch, we recommend using our v2 addon blueprint. For porting existing v1 addons, we refer to the v2 porting guide.

How to try it

  1. Add dependencies:

    yarn add --dev @embroider/core @embroider/compat @embroider/webpack webpack
  2. Edit ember-cli-build.js:

    -return app.toTree();
    +const { Webpack } = require('@embroider/webpack');
    +return require('@embroider/compat').compatBuild(app, Webpack);

    Alternatively, if you are passing optional extra broccoli trees into app.toTree(), you can rewrite like:

    -return app.toTree(extraTreeHere);
    +const { Webpack } = require('@embroider/webpack');
    +return require('@embroider/compat').compatBuild(app, Webpack, {
    +  extraPublicTrees: [extraTreeHere]
  3. Use ember serve, ember test, and ember build as usual.


You can pass options into Embroider by passing them into the compatBuild function like:

return require('@embroider/compat').compatBuild(app, Webpack, {
  // staticAddonTestSupportTrees: true,
  // staticAddonTrees: true,
  // staticHelpers: true,
  // staticModifiers: true,
  // staticComponents: true,
  // staticEmberSource: true,
  // splitAtRoutes: [''], // can also be a RegExp
  // packagerOptions: {
  //    webpackConfig: { }
  // }

The options are documented in detail in Core Options, Compat Options, and Webpack Options.

The recommended steps when introducing Embroider into an existing app are:

  1. First make it work with no options. This is the mode that supports maximum backward compatibility. If you're hitting errors, first look at the "Compatibility with Classic Builds" section below.
  2. Enable staticAddonTestSupportTrees and staticAddonTrees and test your application. This is usually safe, because most code in these trees gets consumed via import statements that we can analyze. But you might find exceptional cases where some code is doing a more dynamic thing.
  3. Enable staticHelpers and staticModifiers and test. This is usually safe because addon helpers and modifiers get invoked declaratively in templates and we can see all invocations.
  4. Enable staticComponents, and work to eliminate any resulting build warnings about dynamic component invocation. You may need to add packageRules that declare where invocations like {{component someComponent}} are getting someComponent from.
  5. Once your app is working with all of the above, you can enable splitAtRoutes and add the @embroider/router and code splitting should work. See the packages/router/ for details and limitations.

Configuring asset URLs

If you are serving your assets from a different origin (like a CDN) from where your index.html content will be served from, you can use the publicAssetURL option to specify the base URL. In pre-Embroider Ember apps, this was accomplished by configuring the fingerprint: { prepend: ... } option handled by broccoli-asset-rev.

return require('@embroider/compat').compatBuild(app, Webpack, {
  packagerOptions: {
    publicAssetURL: EmberApp.env() === 'production' ? '' : '/', // This should be a URL ending in "/"


Ember version

Requires Ember 3.28.11 or greater

With Classic Builds

While we have a strong emphasis on backward compatibility with classic builds, there are a few places where you may need to make changes to your code:

Lazy Engines

If you're using lazy loaded engines, you need to use @embroider/router, which is a drop-in replacement for @ember/routing/router:

-import EmberRouter from '@ember/routing/router';
+import EmberRouter from '@embroider/router';

See @embroider/router README for more details.

Analyzing Bundles





This project is licensed under the MIT License.


Thanks to Cardstack for sponsoring Embroider's development.

Thanks to the Embroider Initiative sponsors for contributing to Embroider's development: