Eslint: add support for class properties

[marcofugaro]

Related issue: #20009 (comment) (remake of #21238)

Description

Eslint also needs to know about babel to support class properties.
In this PR I added @babel/eslint-parser as a parser for eslint. This does not change the current eslint bahaviour.

Third time the charm?

[DefinitelyMaybe]

Third time the charm?

tehe! I been there.

[mrdoob]

Third time the charm?

🤞

[mrdoob]

Seems to be working! Thanks!

[mrdoob]

Unfortunately I have to revert this. Safari doesn't support class properties yet so all examples are currently broken.

[mrdoob]

e7ba155

[marcofugaro]

@mrdoob okay 👍 we'll have to wait then.

We could also choose to transpile build/three.module.js as well, and remove the transpilation step when they will be supported.
BTW now that IE support is dropped, do we still need to transpile three.js and three.min.js? Classes and other es6 features are supported in all modern browsers.

[mrdoob]

BTW now that IE support is dropped, do we still need to transpile three.js and three.min.js? Classes and other es6 features are supported in all modern browsers.

I think I'll wait until importmaps land in browsers.

[marcofugaro]

I think I'll wait until importmaps land in browsers.

We are not using any feature related to import maps in the src/ though, right? 🤔

[mrdoob]

No we are not. But the development experience using three.module.js right now is... problematic.
So until importmaps lands in browser doesn't feel right to force people to move to modules.

[marcofugaro]

I think you misunderstood 🙂 I meant removing the babel transpilation step for three.js and three.min.js.

I am talking about these steps:

three.js/utils/build/rollup.config.js

Lines 343 to 348 in 4d90e23

	babel( {
	babelHelpers: 'bundled',
	babelrc: false,
	...babelrc
	} ),
	babelCleanup(),

The transpilation is just for modern es features (classes, let/const, arrow functions), the conversion from es modules to single umd file that users can use with <script src="three.js"></script> is done by rollup.

[mrdoob]

I misunderstood indeed!

We do still support IE11 in this example:
http://raw.githack.com/mrdoob/three.js/dev/examples/misc_legacy.html

And the current babel setup doesn't seem to cause problems so I see no reason for removing it.