Babel 7 Umbrella

[gaearon]

Want to start documenting things we need to do when Babel 7 is ready.

• Enable runtime transform for helpers with { polyfill: false, useBuiltIns: true, useESModules: true }, see Add useBuiltIns and useESModules options to transform-runtime babel/babel#5442 for context and babel-runtime helpers should not pull in unnecessary polyfills (T7519) babel/babel#4418 for why we couldn't do it before
• We should probably enable transform-inline-elements in production and bundle Symbol polyfill (?).
• Helpers: true (see below)

[Timer]

We'll want to import babel-polyfill by default if we turn useBuiltIns to true.

[gaearon]

Which features would depend on them? I just want to externalize helpers without bringing the whole core-js with them.

[Timer]

useBuiltIns transforms babel-polyfill into only the language features used in the app, babel-polyfill would become a single core-js import of Map if that's the only feature used.

[Timer]

To clarify, I made the suggestion to make the development experience nicer; not that we need it.

[gaearon]

Hmm, that's not the part of useBuiltins I'm interested in. IMO trying to guess needed features by code is always lossy ([].includes) and we shouldn't attempt that.

The thing I'm interested in is deduplicating Babel helpers like _createClass. It's possible today with helpers: true but this brings in core-js due to how Babel worked (babel/babel#4418). As I understand this is now fixed.

[Timer]

IMO trying to guess needed features by code is always lossy ([].includes) and we shouldn't attempt that.

This works in Babel 7 from what I was told. As does many other really obscure cases:

'abc'['inclu' + 'des']('a')

I haven't actually tested this myself, but it would be sweet if it did.

---

Unfortunately, I don't think we can opt-out of this behavior for end-users that end up requiring babel-polyfill. Is useBuiltins required as part of deduping these helpers?

[badsyntax]

This works in Babel 7 from what I was told. As does many other really obscure cases:

I put together an example project showing how this works, by using the "useBuiltIns": "usage" option of @babel/env: https://github.com/badsyntax/babel-builtin-polyfills

[gaearon]

Now might be a good time to start trying Babel 7 and looking out for issues.