Ember Support

tsdown can build Ember v2 addons (libraries) with @nullvoxpopuli/ember-rolldown. This meta-plugin compiles .gts and .gjs files, including their <template> tags, into publishable output. A single ember() call replaces the usual @embroider/* externalization setup, content-tag preprocessing, and Babel integration.

NOTE

The plugin currently targets Ember libraries (v2 addons); building Ember apps has not been tested.

Minimal Example

Configure an Ember library in tsdown.config.ts as follows:

tsdown.config.ts

import { ember } from '@nullvoxpopuli/ember-rolldown'
import { defineConfig } from 'tsdown'

export default defineConfig({
  entry: ['./src/index.ts'],
  dts: true,
  plugins: [ember()],
})

Create a typical Ember component:

src/components/badge.gts

import type { TOC } from '@ember/component/template-only'

export interface BadgeSignature {
  Element: HTMLSpanElement
  Args: { label: string }
  Blocks: { default: [] }
}

export const Badge: TOC<BadgeSignature> = <template>
  <span class="badge" ...attributes>
    {{@label}}
    {{yield}}
  </span>
</template>

And export it from your entry file:

src/index.ts

export { Badge } from './components/badge.gts'

The build writes .js and .d.ts files for each entry to dist/ and emits source maps for the JavaScript output. Ember virtual packages (such as @ember/component and @glimmer/tracking) and packages listed in dependencies or peerDependencies remain external and are resolved by the consuming app.

Install the required dependency:

npm

npm install -D @nullvoxpopuli/ember-rolldown

pnpm

pnpm add -D @nullvoxpopuli/ember-rolldown

yarn

yarn add -D @nullvoxpopuli/ember-rolldown

bun

bun add -D @nullvoxpopuli/ember-rolldown

NOTE

@nullvoxpopuli/ember-rolldown requires Node.js 24+. Because the package ships TypeScript source, type-checking a project that uses it also requires TypeScript 6+ and a lib setting that includes es2025 (for example, esnext).

Declarations

.gts and .gjs template-tag modules exist only in the bundler's module graph, so their declarations must be generated with isolated declarations. The tsconfig used for the build must enable isolatedDeclarations; otherwise, ember() reports an error:

tsconfig.json

{
  "compilerOptions": {
    "isolatedDeclarations": true,
  },
}

isolatedDeclarations requires sufficient type annotations on exports so declarations can be generated without cross-file type inference. For example, the component above uses the explicit TOC<BadgeSignature> type annotation. If your package also contains development-only code that should not be subject to this constraint, such as a demo app or in-package tests, point the tsdown tsconfig option to a publish-only config:

tsdown.config.ts

export default defineConfig({
  entry: ['./src/index.ts'],
  tsconfig: './tsconfig.publish.json',
  plugins: [ember()],
})

How It Works

ember() returns a set of Rolldown plugins that:

• Keep packages from dependencies and peerDependencies, along with Ember virtual packages, external for the consuming app to resolve.
• Preprocess <template> tags with content-tag and map .gts/.gjs to .ts/.js so Rolldown can process them.
• Run Babel only on files that need it, such as files with template tags or decorators. All other files use Rolldown's fast native transforms.
• Verify that the tsconfig enables isolatedDeclarations.

A Babel configuration is optional. Without one, ember() uses built-in defaults to handle templates, decorators, and TypeScript. If you provide one, ember() uses it instead.

CSS

If a component imports co-located CSS (import './badge.css'), install @tsdown/css in your project. tsdown detects the package automatically and bundles imported stylesheets into a single CSS file in dist/. Set css: { inject: true } to preserve an import for that generated CSS file in the JavaScript output, allowing consuming apps to load the styles through the module graph.

For advanced topics such as app re-exports for classic name-based resolution, ember-scoped-css integration, and publish-specific Babel configurations, see the plugin documentation.