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Aurelia BEM

Helper library to work with BEM classes in Aurelia


<div class="${bem('my-component', null, 'light')}">
  <div class="${bem('my-component', 'my-element', ['active', 'opaque'])}"></div>

results in

<div class="my-component my-component--light">
  <div class="my-component__my-element my-component__my-element--active my-component__my-element--opaque"></div>


You will find a sample app inside dev-app which gets started with npm start. Besides using this plugin it also makes use of:

  • StyleLint + StyleLint-Sass
  • The Bem naming convention applied + preconfigured rules for StyleLint
  • Scss with the latest Sass modules feature (@use)
  • The Aurelia task updated to make use of gulp-dart-sass as node-sass currently doesn't support the modules feature

Make sure to have your VSCode updated to the latest November release for proper support of the new Sass feature


This project is bootstrapped by aurelia-cli.

This Aurelia plugin project has a built-in dev app (with CLI built-in bundler and RequireJS) to simplify development.

  1. The local src/ folder, is the source code for the plugin.
  2. The local dev-app/ folder, is the code for the dev app, just like a normal app bootstrapped by aurelia-cli.
  3. You can use normal au run and au test in development just like developing an app.
  4. You can use aurelia-testing to test your plugin, just like developing an app.
  5. To ensure compatibility to other apps, always use PLATFORM.moduleName() wrapper in files inside src/. You don't need to use the wrapper in dev-app/ folder as CLI built-in bundler supports module name without the wrapper.

Note aurelia-cli doesn't provide a plugin skeleton with Webpack setup (not yet), but this plugin can be consumed by any app using Webpack, or CLI built-in bundler, or jspm.

How to write an Aurelia plugin

For a full length tutorial, visit Aurelia plugin guide.

Here is some basics. You can create new custom element, custom attribute, value converter or binding behavior manually, or use command au generate to help.

au generate element some-name
au generate attribute some-name
au generate value-converter some-name
au generate binding-behavior some-name

By default, the cli generates command generates files in following folders:


Note the folder structure is only to help you organising the files, it's not a requirement of Aurelia. You can manually create new element (or other thing) anywhere in src/.

After you added some new file, you need to register it in src/index.ts. Like this:

  // ...

The usage of PLATFORM.moduleName wrapper is mandatory. It's needed for your plugin to be consumed by any app using webpack, CLI built-in bundler, or jspm.

Resource import within the dev app

In dev app, when you need to import something from the inner plugin (for example, importing a class for dependency injection), use special name "resources" to reference the inner plugin.

import {autoinject} from 'aurelia-framework';
// "resources" refers the inner plugin src/index.ts
import {MyService} from 'resources';

export class App {
  constructor(myService: MyService) {}

Manage dependencies

By default, this plugin has no "dependencies" in package.json. Theoretically this plugin depends on at least aurelia-pal because src/index.ts imports it. It could also depends on more core Aurelia package like aurelia-binding or aurelia-templating if you build advanced components that reference them.

Ideally you need to carefully add those aurelia-pal (aurelia-binding...) to "dependencies" in package.json. But in practice you don't have to. Because every app that consumes this plugin will have full Aurelia core packages installed.

Furthermore, there are two benefits by leaving those dependencies out of plugin's package.json.

  1. ensure this plugin doesn't bring in a duplicated Aurelia core package to consumers' app. This is mainly for app built with webpack. We had been hit with aurelia-binding v1 and v2 conflicts due to 3rd party plugin asks for aurelia-binding v1.
  2. reduce the burden for npm/yarn when installing this plugin.

If you are a perfectionist who could not stand leaving out dependencies, I recommend you to add aurelia-pal (aurelia-binding...) to "peerDependencies" in package.json. So at least it could not cause a duplicated Aurelia core package.

If your plugin depends on other npm package, like lodash or jquery, you have to add them to "dependencies" in package.json.

Build Plugin

Run au build-plugin. This will transpile all files from src/ folder to dist/native-modules/ and dist/commonjs/.

For example, src/index.ts will become dist/native-modules/index.js and dist/commonjs/index.js.

Note all other files in dev-app/ folder are for the dev app, they would not appear in the published npm package.

Consume Plugin

By default, the dist/ folder is not committed to git. (We have /dist in .gitignore). But that would not prevent you from consuming this plugin through direct git reference.

You can consume this plugin directly by:

npm i github:your_github_username/aurelia-bem
# or if you use bitbucket
npm i bitbucket:your_github_username/aurelia-bem
# or if you use gitlab
npm i gitlab:your_github_username/aurelia-bem
# or plain url
npm i https:/

Then load the plugin in app's main.ts like this.

// for webpack user, use PLATFORM.moduleName wrapper

The missing dist/ files will be filled up by npm through "prepare": "npm run build" (in "scripts" section of package.json).

Yarn has a bug that ignores "prepare" script. If you want to use yarn to consume your plugin through direct git reference, remove /dist from .gitignore and commit all the files. Note you don't need to commit dist/ files if you only use yarn to consume this plugin through published npm package (npm i aurelia-bem).

Publish npm package

By default, "private" field in package.json has been turned on, this prevents you from accidentally publish a private plugin to npm.

To publish the plugin to npm for public consumption:

  1. Remove "private": true, from package.json.
  2. Pump up project version. This will run through au test (in "preversion" in package.json) first.
npm version patch # or minor or major
  1. Push up changes to your git server
git push && git push --tags
  1. Then publish to npm, you need to have your npm account logged in.
npm publish

Automate changelog, git push, and npm publish

You can enable npm version patch # or minor or major to automatically update changelog, push commits and version tag to the git server, and publish to npm.

Here is one simple setup.

  1. npm i -D standard-changelog. We use standard-changelog as a minimum example to support conventional changelog.
  1. Add two commands to "scripts" section of package.json.
"scripts": {
  // ...
  "version": "standard-changelog && git add",
  "postversion": "git push && git push --tags && npm publish"
  1. you can remove && npm publish if your project is private

For more information, go to

Run dev app

Run au run, then open http://localhost:9000

To open browser automatically, do au run --open.

To change dev server port, do au run --port 8888.

To change dev server host, do au run --host

PS: You could mix all the flags as well, au run --host --port 7070 --open

Unit tests

Run au test (or au jest).

To run in watch mode, au test --watch or au jest --watch.