Enhancement/issue 187 polyfills plugin

[thescientist13]

Related Issue

resolves

• Polyfills Plugin #187
• have polyfills in index.html managed as npm dependencies #178
• postcss-cssnext has been deprecated #140

Summary of Changes

1. Created a Polyfills Plugin - currently enabled by default for now, will follow up as part of Polyfills plugin should feature detect polyfills support (using webcomponents loader) #9 and decouple polyfills for serialization from polyfills needed for users #193
2. Refactored Babel transpilation implementation to be based on modern @babel/preset-env configuration (@babel/polyfills deprecated)
3. Pulling webcomponents from npm now - have polyfills in index.html managed as npm dependencies #178
4. Upgraded to postcss-preset-env - postcss-cssnext has been deprecated #140
5. IE11 supported by default (though somewhat broken in places - see TODOs)
6. Created some How It Works and Browser support docs
7. Since polyfills from node_modules are required for now, adjusted TestBed to support this hard dependency
8. Misc contributor documentation for IE testing
9. Fixed hooks naming convention
10. Better documentation for Plugin APIs

TODO

1. Hmm.. tests are passing locally 🤔 re ran the build in CircleCI and everything passed ✅
2. Document config and context usage in docs ✅
3. There are minor bugs with IE11 / Edge that I need to open, otherwise site looks good! ✅
   • CSS variables for Edge?
   • Edge and develop
   • IE11 home page
4. This definitely helped bring bundle sizes down a little and improve lighthouse (though we can definitely do better). Will run Lighthouse and hopefully [RFC] Route Based Code Splitting #136 will help with our initial payload sizes being larger than I would like. Will probably make a ticket for that too, or update the description of the code splitting ticket. Updated Code Splitting description ✅
5. Will be good to discuss Polyfills plugin should feature detect polyfills support (using webcomponents loader) #9 and decouple polyfills for serialization from polyfills needed for users #193 during our weekly call ✅

[thescientist13]

Regarding the initial build failure and subsequent passing by just re-running the build, going to see if re-running the build a few more times corroborates any particular outcome. One thought is that I introduced more sync based file operations as part of TestBed so maybe Node had a bit of an issue? I know often times the NodeJS docs say to use use the async (default) versions of these fs methods.

Anyway, will run it 3 more times and see what it's like. Could just be a one-off that occurs sometimes like any sort of system / networking / etc.

[thescientist13]

Reran the build three more times and everything seems to be running fine