[Planned] adjust transpilation target above es5

[kwonoj]

This is definitely semver major breaking changes discussion.

With Windows 7 EOL, IE11 is also considered as EOL. There are still in-use customers like few enterprise companies, but it won't get a major update in features at all.

Currently, rxjs targets transpilation target's set to es5, conservative runtime output to support most of browsers. This issue is to discuss

• potentially raise transpilation target above es5, to reduce transpilation runtime
• declare few browser support deprecation

1. What target should we aim for?

This depends on major browser usage across consumers, but probably best is set to ES2015 to aim conservative target (again).

2. What about old browsers (IE11)?

Consumer aims to make application to use those browser may need additional configuration on their bundler to downlevel transpilation to rxjs.

3. Should we do this now? why?

Maybe not, just open for discussion (in related with native esm support changes I'm trying to tackle).

[kwonoj]

Core team has reached general agreement to pursue this. Current planned roadmap as written below, still subject to change depends on ecosystem / user feedback.

• 7.x : no transpilation target adjustment
• 8.x : cjs / esm will adjust transpile target to 2015 as semver breaking major
• beyond 9: potential exploration to taget esm as native (current esm is equivalent to cjs transpiled output but only preserves es import syntax). this is TBD.

[JeanMeche]

Looks like right now, v8 will ship ES2022 ESM code right ?

[kwonoj]

Yes, that's the plan so far.