According to the `nextjs` documentation, if I want to [expose my environment variables to the browser](https://nextjs.org/docs/basic-features/environment-variables#exposing-environment-variables-to-the-browser) I can just prefix them with `NEXT_PUBLIC` in my `.env.local` file, like so:

```
NEXT_PUBLIC_VAR=7

```

However, it looks like I can *also* expose my environment variables to the browser by using `next.config.js`, like so:

```js
module.exports = {
  env: {
    PUBLIC_VAR: process.env.PUBLIC_VAR,
  },
}

```

And this will [add to the javascript bundle](https://nextjs.org/docs/api-reference/next.config.js/environment-variables)

What is the difference between these two strategies?