Switch to Typescript incrementally (test runs ts-node)

[rosskevin]

Supersedes #9517. See #9517 for details.

What's left

• a few broken tests (1-5 depending on the run)
• next.js build issue (details below)

Completed

• js/ts/tsx all work in mocha
• converted internal utils/styles etc to ts
• converted a few components for testing
• converted a few specs for testing
• fixed known build issues - yarn build runs - updated to babel 7. Effectively, we use tsc like we did flow, and tsc is uninvolved in the build process (but a required precursor).

[rosskevin]

And there we have a problem with ts/babel - imports again. import = require is not supported by babel (and shouldn't be). This is a workaround for non-es non-default exports as I understand it.

SyntaxError: src/transitions/Slide.tsx: `import =` is not supported.

@pelotom thoughts on getting around this with babel for compilation? Perhaps there are other options than import = require than I am aware?

https://www.typescriptlang.org/docs/handbook/modules.html#export--and-import--require

I filed babel/babel#7062 but I think we'll likely need to use tsc to process to es2015 first.

[rosskevin]

The prettier issue is fixed - I didn't change the parser.

[rosskevin]

Note - I have a potential fix for import = @require - trying it out now.

[rosskevin]

build:es is working - first pass through the code with babel complete.

[rosskevin]

yarn build works 😄

We are just a bit closer.

[pelotom]

FYI, you don’t need the : Theme annotation since you declared the overall type of styles.

[rosskevin]

Done thanks.

[rosskevin]

It looks like next.js added jsx support 14 days ago in vercel/next.js#3376

I assume next.js would need to be using babel 7 first (this babel 7 PR has gone uncommented vercel/next.js#3428). And if using babel 7, then there doesn't seem to be any reason why ts|tsx wouldn't work with the way we have approached this and changes just like they did for jsx. I added a comment on the next.js issue vercel/next.js#2391 (comment)

[rosskevin]

Closing in favor of #9561. If we want to go back to using ts-node, I'll have to re-apply those changes there.