Frontend Development

Home Assistant uses Polymer for the UI and NuclearJS for maintaining the app state.

Do not use development mode in production. Home Assistant uses aggressive caching to improve the mobile experience. This is disabled during development so that you do not have to restart the server in between changes.

Setting up the environment

Home Assistant will by default serve the compiled version of the frontend. As everything is compiled into the file frontend.html you do not want to work with the compiled version but with the separate files during development. To enable development mode for Home Assistant, update your configuration.yaml to have these lines:

  development: 1

Node.js is required to setup the frontend development environment. The preferred method of installing node.js is nvm. Install nvm using the instructions in the README, and install node.js by running the following command:

$ nvm install node

Next step is to get the frontend code. When you clone the Home Assistant repository, the frontend repository is not cloned by default. You can setup the frontend development environment by running:

$ script/setup


While you are developing, you need to have Rollup running to have your JavaScript changes be made available.

$ cd homeassistant/components/frontend/www_static/home-assistant-polymer
$ npm run js_dev

The source code for the frontend can be found in three different directories:

  • UI: homeassistant/components/frontend/www_static/home-assistant-polymer/src/
  • Core: homeassistant/components/frontend/www_static/home-assistant-polymer/home-assistant-js/src/
  • Panels: homeassistant/components/frontend/www_static/home-assistant-polymer/panels/

Building the Polymer frontend

Building a new version of the frontend is as simple as running script/build_frontend. This fires off the following commands:

  • home-assistant-polymer: Install NPM dependencies.
  • home-assistant-polymer: start frontend build.
    • Compile all used JavaScript.
    • Install Bower dependencies.
    • Vulcanize and minify the core and panel sources to build dir.
  • Copy the webcomponents polyfill webcomponents-lite.min.js from home-assistant-polymer to components/frontend/www_static/webcomponents-lite.min.js.
  • Copy the final frontend build frontend.html and panel sources from home-assistant-polymer to components/frontend/www_static/frontend/.
  • Generate MD5 hashes of core and panel sources.
  • Create gzip versions of all the sources.