Custom Rules - using an another npm module

I see in the documentation the following:

“If you have any module system, you need to use some bundler, preferably Rollup.js as it generates efficient bundles. We are still evaluating the idea of supporting ESModule and perhaps we will decide to bring support for ES Modules at some point, yet for now you cannot use them.”

link

I could not find an open issue in github for the above statement.

I’ve played with rollup.js and the library I want to use requires file system access so even an ‘iife’ is not going to work.

Are there any other options?

Thanks,

Mark