Add ES-modules build

[goto-bus-stop]

Hi 👋 Thanks for y'all's work on redux-actions, it's very useful :)

I do have a small proposal: to publish an ES-modules build as well, for bundlers like Rollup and Webpack2.

This patch conditionally enables the transform-es2015-modules-commonjs transform based on an env var. All the environment setup in the npm scripts is getting a little messy this way, though, because the transform needs to be enabled in all cases except one. I don't think there's a way to conditionally disable a transform in a .babelrc unfortunately :(

---

What I could do instead is add a "custom" preset that determines whether to set the modules property based on an env var:

// build/preset.js
const esModules = process.env.BABEL_ENV === 'es'
module.exports = {
  presets: [
    ['es2015', { modules: esModules ? false : 'commonjs' }]
  ]
}

// .babelrc
{
  "presets": [
    "./build/preset",
    "stage-0"
  ]
}

That would keep the npm scripts more clean. If that sounds better, let me know!

[yangmillstheory]

👋

Thanks. I'm out today, but can take a look tonight 👍.

[yangmillstheory]

Wait, could you illustrate what problem this is trying to solve?

I use ES2015 modules with Webpack, so I don't think I've run into the use case.

[goto-bus-stop]

It already works fine with Rollup and Webpack2, but they can't apply tree-shaking to the CommonJS module. Also, there's duplicate module interop code: Babel's requireInterop code, and then Rollup or another bundler's glue code to make CommonJS work with their preferred format.

With this PR, bundlers that support ES modules can tree-shake: if Rollup builds a project that is eg. not using the createActions method anywhere, it won't be added to the bundle (and neither will the lodash methods that createActions depends on). And module bundlers that don't support ES modules natively will just keep using the CommonJS build.

[yangmillstheory]

Can we try the build/preset.js approach, since it seems like it'd be cleaner?

[goto-bus-stop]

Sure! Added :)

[yangmillstheory]

What is this module key for? Couldn't find anything about it.

[goto-bus-stop]

module serves about the same purpose as jsnext:main and is used by webpack2 and Rollup. I went by this Rollup wiki page which says

If in doubt, use both!

[yangmillstheory]

It looks like commonjs is the default, so how about

const esOptions = process.env.BABEL_ENV === 'es' ? { modules: false } : {}

That way we don't have to hardcode commonjs and we can just use Babel defaults.

[yangmillstheory]

Why are we linting build/? Is there even a build/ directory?

[goto-bus-stop]

It's for the new build/preset-es2015.js file.

[yangmillstheory]

I wonder if it's worth including a comment (or modifying the existing) in this section of the README on the ES2015 build. Thoughts?

[yangmillstheory]

Thanks @goto-bus-stop. I'll publish v1.2.0 shortly.

[yangmillstheory]

https://github.com/acdlite/redux-actions/releases/tag/v1.2.0 has been published.