Add an --es-modules option

[milesj]

Feature Request

Is your feature request related to a problem? Please describe.

Babel is great at compiling to a single target, but not so great at compiling multiple targets with different configurations, for example, when compiling an ES5 target (main lib/) and an ES5 target with ES6 imports/exports (module esm/, which is required for tree shaking).

At the moment, this can be achieved with env variables, double builds, and some conditional statements within the babel configuration. However, it is a bit clunky.

"build": "npm run build:lib && npm run build:esm",
"build:lib": "babel ./src --out-dir ./lib",
"build:esm": "ESM=true babel ./src --out-dir ./esm",

Describe the solution you'd like

The options required for ESM builds are modules: false (and possibly targets.esmodules) in preset-env and useESModules: true in plugin-transform-runtime. It would be nice to be able to pass a CLI option that turns on all ES module related options.

"build": "babel ./src --out-dir ./lib && babel ./src --out-dir ./esm --es-modules",

Describe alternatives you've considered

A true parallelized multiple targeting system that is ran through a single babel command.

targets: [
  { outDir: './lib' },
  { outDir: './esm', esModules: true, plugins: [], presets: [] },
],

Teachability, Documentation, Adoption, Migration Strategy

Will write if considered.

[babel-bot]

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