The two versions of bundles are:

1. Modern bundle: targeting modern browsers that support ES modules
2. Legacy bundle: targeting older browsers based on babel config (IE9 compatible by default).

package.json

• Nuxt will automatically detect modern build in when modern is not specified, auto-detected mode is:

• Modern mode for nuxt generate can only be client
• Use to set crossorigin attribute in <link> and <script>

Please refer Phillip Walton’s excellent post for more knowledge regarding modern builds.