Introduce TypeScript support into the dev & build systems

[chandlerprall]

Summary

closes #1262

• TypeScript support within the EUI codebase (src, src-docs, and tests).
• Prop definitions for React components are transpiled to React propTypes with a custom babel plugin
• Spacer component, its test, and docs have been converted
• common, required_props, and the predicates service have been converted

Checklist

- [ ] This was checked in mobile
- [ ] This was checked in IE11
- [ ] This was checked in dark mode
- [ ] Any props added have proper autodocs

• Documentation examples were added
• A changelog entry exists and is marked appropriately
• This was checked for breaking changes and labeled appropriately
• Jest tests were updated or added to match the most common scenarios
  - [ ] This was checked against keyboard-only and screenreader scenarios
  - [ ] This required updates to Framer X components

[pugnascotia]

Is there a plan for migrating components to TS? Will you / we / someone just work through them in a series of PRs? I can help if you like.

[chandlerprall]

Have these changes been tested against Kibana?

I've tested them briefly in Kibana, doing more today & tomorrow.

Hmm, I'm now wondering if EUI is not very amenable to linking. Same issue when I switch to master.

I'm not sure what happened to make linking unhappy (it's something about the nested-nested node_modules in EUI), but I've started following this pattern:

• in eui: npm pack creates a tarball in working dir with the files that would be published
• extract tarball somewhere else (I do my home directory), will extract to a directory named package
• yarn install ~/package (or whatever your path to the extracted package dir is
• yarn has now installed the eui package as it would have been installed, just from a directory instead of npm

Is there a plan for migrating components to TS? Will you / we / someone just work through them in a series of PRs? I can help if you like.

I'm putting together a screencast walkthrough of the EuiSpacer conversion to help bring people up to speed. The plan is then a series of PRs - I was planning on putting a script together that can list the next candidates for conversion as we have to do a bottom-up approach to avoid importing a JS file into TS.

[jasonrhodes]

• extract tarball somewhere else (I do my home directory), will extract to a directory named package

FWIW, this npm pack process only worked for me when I did yarn install PATH and PATH pointed at the tarball created by npm pack directly, without extracting it. Which also was one less step!

[pugnascotia]

Added comments look good.

[snide]

This is fantastic. I tested everything by converting a component in TS. chandlerprall#7

Only other comment I'd make other than the ones below is that we should update the Yeoman scripts to build TSX files and docs for new components. If that's time consuming I'm OK merging this now and making it a separate PR.

[snide]

We should cement this as a pattern. Your vid had you redeclaring the default prop value, which I'm sure people might do since it's clean, but let's make sure we do the ternary check in review so we don't have dupe values.

[chandlerprall]

@jasonrhodes @pugnascotia @snide

Thank you all for your help on this; I've pushed up the final requested changes (yeoman template update, small docs codegen change). I'll merge this Friday morning Eastern Time unless anything else is mentioned.

[snide]

Cool. I'll give the new stuff a check.

[chandlerprall]

jenkins test this

[chandlerprall]

jenkins test this