ES6 code in production build breaks IE11

I was hoping to give Recoil a try in one of my projects, but it looks like ES6 code is not being transpiled away in the production build:

const next=new Set(set);
class AbstractRecoilValue{constructor(newKey)

We sadly have to support IE11, would it be possible to update the rollup config to output ES5 code instead?

[mondaychen]

Let’s add ES5 transpiling in a separate PR (after #433 merged) so that we can test the impact on file size there.

Some thoughts on the options we have:

About loose mode: IMO we should NOT use babel loose mode because this is a library and we should not risk getting problems when switching to non-transpiled version in the future.

About providing multiple outputs: if we do see a relatively significant size impact in the output transpiled down to es5, we can consider providing one single ES-current uncompressed output, so that people who care about size a lot have the option to pick target browsers themselves.

[Brianzchen]

@mondaychen I’ve checked out on my local and linked to my app. Seems to all work as expected without any random import errors that I had before.

But it’s still not transpiled down to es5. That would simple just to add @babel/preset-env, should we add it to #433 or have a separate PR?