A mininum boilerplate to deliver a Polymer 3.x with Webpack, PostCSS and Service Workers ready. Made for personal use, glad if someone can get a good starting point from here. Bye bye Bower.

• Webpack
• webpack-dev-server with hot reloading active.
• PostCSS with many plugins.
• Service Workers generated by Workbox through the workbox-webpack-plugin (just for build)
• Copy statics file on dist folder (like vendor/webcomponents-loader.js and others)
• standard-version is bundled for managing versioning and changelogs.
• ES6 modules bundle and ES5 transpiled bundle both handled using the new nomodule and type=module feature of modern browsers. Learn more on how to ship ES6 modules today in production.

• babel-loader with the babel-preset-env enabled for the last 2 versions and babel-plugin-transform-object-rest-spread installed.
• text-loader - Load HTML templates as string.
• postcss-loader - Load PostCSS into the <style> scoped tag of Polymer elements as string.

All modern browsers. 🕶

But as the features said, we are also transpiling the bundle for "oldie" browsers. Of course we are not covering things like IE11.

Clone this repository:

git clone https://github.com/PolymerX/polymer-skeleton [your-app-name]

Remove the .git folder and change details within:

• package.json
• src/manifest.json

Then start building your application!

yarn

Start the webpack-dev-server on localhost http://localhost:3000 with hot-reload and watch on .pcss files.

For "oldie" browsers, transpiling also Javascript class. Works on Firefox:

yarn dev

For modern browsers with class support. Works on Chrome, Safari, and Edge:

yarn dev:module

XO for code style, Stylelint for PostCSS linting, and WCT for components tests:

yarn test

Run Lighthouse for testing the PWA capabilities:

yarn test:lighthouse

(Almost) production-ready (webpack --optimize-minimze and copy statics) to dist folder. Also generating Service Workers. The command will also create the module version of the bundle ready to be loaded as type=module.

yarn build

During development .pcss files will be watched, compiled and injected to the relative <style> tag within the component template. The CSS is scoped to the component so don't worry about CSS specificity, you can also use :host, :host-context and :root selectors. Read more about styling web components and custom CSS properties.

We also include Autoprefixer plugin, if you don't know how it works (...and you should), it allows you to write CSS without worrying about vendor prefixes. Just write your css properties prefix-free and let autoprefixer do the work for you when compiling.

How about commons styles? You can simply import any other .pcss file within your main component .js file and print it inside the template().

We are getting the webpcomponents-loader.js polyfill from GitHub using NPM/Yarn and copying it into a vendor folder with a Node script.

Loading the custom-element-es5-adapter.js is necessary because the custom elements known(1) issue(2) (the lovely Uncaught TypeError: Class constructor PolymerElement cannot be invoked without 'new') about ES6 classes, but just on old browsers.

PolymerX © MIT