Mix-manifest always prefixed with public

I am running this in a custom project outside of Laravel. I have tried multiple things but the manifest always creates paths with public prefixed:

{
  "public/js/app.js": "public/js/app.ee0ab4b45edac1e84a9d.js",
  "public/css/app.css": "public/css/app.e937875be4a33e00472a.css"
}

My mix file:

mix.js('resources/assets/js/app.js', 'public/js')
  .sass('resources/assets/sass/app.scss', 'public/css')
  .version();

In Laravel the mixfile looks exactly the same yet produces a mix-manifest without the public prefix. I have also looked at the mix() helper in Laravel what am I missing here?

[JeffreyWay]

For a stand-alone project, you need to tell Mix what your public base directory is. Do:

mix.js('resources/assets/js/app.js', 'public/js')
  .sass('resources/assets/sass/app.scss', 'public/css')
  .version()
  .setPublicPath('public');

[JeffreyWay]

The mix-manifest.json file should always be in your public directory.