Add optional chaining and nullish coalescing operators support

[renatoagds]

Since optional-chaining and nullish coalescing has been moved to Stage 3, we're now able to add them to CRA.

Closes #7431

[existentialism]

We should wait until babel/babel#10269 lands and is released.

[mrmckeb]

Agreed @existentialism.

It's also important to note that TypeScript users will need to wait until TypeScript 3.7 lands, as TypeScript 3.6 is feature-complete. Which is sad, as I want to use it now - but great that the TS team is on top of this.

[yasso1am]

How does one go about updating a project created with CRA2 with typescript to include the optional chaining and nullish operator?

[mrmckeb]

@yasso1am, please see the comment right before yours. We're waiting on this still from the TS team.

[montogeek]

@mrmckeb TS team progress is a blocker to merge and release this change?

[montogeek]

@renatoagds Could you please fix merge conflict issues to keep this PR ready to merge? :)

[renatoagds]

@montogeek as soon babel/babel#10269 get released I'll update here.

[leepowelldev]

Keen to see this land

[eladmotola]

@renatoagds babel 7.6.0 came out an hour ago with this change

[a-tokyo]

Excited for this!! 🎉

[mlshv]

I think it is now ready to be shipped

[ianschmitz]

We will ship once TypeScript includes support.

[montogeek]

This shouldn't wait for TS support, yes, CRA supports TS, but it shouldn't be a blocker for the JavaScript ecosystem. Please release it.

[topaxi]

@montogeek I kinda agree, but there might arise issues where standalone JS files work fine, but once a TS file imports a JS file with unsupported syntax things might go wrong.

[mAAdhaTTah]

Does TS actually import / parse .js files? I thought it just used .d.ts files next to them?

[topaxi]

Yes it does, it can infer some basic shapes of classes/objects and even parse and use jsdoc type annotations.

[yordis]

This is when I wish people lock the thread.

Everyone from the CRA knows what to do about this and when.

And from now on,

Only people complaining or pointing on obvious things (like it is ready from Babel, just read the thread please) will creating unnecessary notifications.

[ianschmitz]

A reminder that we'll want to bump the plugin versions including @typescript-eslint/* before releasing this

[iansu]

Even though the TypeScript 3.7 beta is now available this still won't work properly. typescript-eslint does not have support for parsing the new syntax yet: typescript-eslint/typescript-eslint#1033

[iansu]

We are now waiting on Prettier support, which is tracked here:

prettier/prettier#6595
prettier/prettier#6609

[ianschmitz]

Thanks @renatoagds!

I'll add tests in a follow-up PR.