Stop publishing rxjs-es. Move ES6 build to output .mjs files alongside the CJS .js files.

[benlesh]

In speaking with @robwormald the Angular folks are forced to swap between rxjs and rxjs-es during their build to enable proper tree-shaking. This is probably less than ideal. If all of the es6 files were under the same directories as .mjs files, then it would be as easy as configuring the bundler to look at that file extension to use ES6 modules.

This would mean that the rxjs-es build would likely not have a use anymore.

cc/ @IgorMinar @jeffbcross @bradlygreen

[jayphelps]

I'm not big on jumping on the .mjs bandwagon so dang soon, particularly since it is so controversial..it's far from decided.

That said, if we did publish .mjs files alone alongside the .js CJS files, it wouldn't hurt anyone but ourselves down the road if the .mjs thing dies but people are still depending on rxjs supporting it. So if we're OK with committing to support it even if .mjs dies (at least for a transitional period), then I'm not otherwise against it.

Also--I do not think we should stop publishing rxjs-es regardless because there will definitely be people who don't subscribe to the .mjs pitch but still want to consume the raw ES6 module version via standard .js extensions.

[robwormald]

should be clear - i'm not advocating at all the .mjs bandwagon - in fact we're currently on the jsnext:main bandwagon (via rollup) - which ideally has es6 sources distributed in a subfolder of the cjs distro and a field in the package.json pointing at it's entry point.

Sigh.

[jayphelps]

@robwormald Great clarification, I didn't realize that. oy vey module systems...

I'm way more OK with including the source as ES6 modules w/ .js extensions inside the normal rxjs CJS package, but inside a dir like es6/*.js and then pointing jsnext:main to it.

esm might be a better dir name since I believe we want to transpile al the syntax to ES5 except the module syntax.

[jayphelps]

Just to make things more interesting, TypeScript does not currently support targeting ES5 but keeping ES6 module syntax. e.g. tsc --target es5 --module es6 doesn't work.

Open issue: microsoft/TypeScript#6319

Sooooo...we could output entirely ES6 code, but then you must transpile all ES6 syntax, not just the module syntax. Is that OK? AFAIK rollup only supports the module syntax, not all of ES6 so you'd need an additional transpilation step in between......

[jayphelps]

hahaha actually, we could build esm/*.js files by building rxjs in TS -> ES6 then pipe that into babel to output ES5 w/ ES6 module syntax...gawd help us.

[robwormald]

we (currently) figure that just outputting full on ES6 code there is probably fine for the moment. Note that latest versions of TS allow .js input with --allowJs so you can use a single tool across the chain - i'm currently doing TS -> ES6 -> rollup -> ES5 via tsc.

[robwormald]

We're doing the esm subdir thing. Makes as much (or as little...) sense as anything right now

[benlesh]

So, @robwormald and @jayphelps ... are we currently, then, proposing to moving to build everything out into one package?

Basically, what we currently publish to rxjs (which is the CJS files), but also with an esm folder? (and perhaps a ts folder, I guess?)

In turn, we'd have one UMD output, and would no longer produce a special AMD bulid?