The current code will give a list of all files in a folder, assuming it's on the server side you want to list all files:

var fs = require('fs');
var files = fs.readdirSync('/assets/photos/');

No, Javascript doesn't have access to the filesystem. Server side Javascript is a whole different story but I guess you don't mean that.

I write a file dir.php

var files = <?php $out = array();
foreach (glob('file/*.html') as $filename) {
    $p = pathinfo($filename);
    $out[] = $p['filename'];
}
echo json_encode($out); ?>;

In your script add:

<script src='dir.php'></script>

and use the files[] array