cheap node 14 native esm support with wrapper.mjs

So you've got a package that already works in the ecosystem and node v14 with its native ESM support is about to go LTS and you've got users asking you to support node v14+ native ESM.

Here's the cheap way: wrap it.

In package.json, use conditional exports to point at a wrapper.mjs for import and your usual main export for require.

{
  "exports": {
    "import": "./wrapper.mjs",
    "require": "./dist/index.js"
  }
}

Then in the new wrapper.mjs take advantage of node's commonjs/esm interop to re-export the exports. Note that you will have to import the default export for commonjs compatibility reasons.

import Pkg from './dist/index.js';

export const thing = Pkg.thing;
export const another = Pkg.another;