index.html

Your serial ports:
<ul id="ports"></ul>

<script>
  require('serialport').list(function(err, ports){
    document.getElementById('ports').innerHTML = ports.map(function(port){
      return '<li>' + port.comName + '</li>';
    }).join('');
  });
</script>

package.json

{
  "name": "nwktest",
  "version": "1.0.0",
  "devDependencies": {
    "node-webkit-builder": "^0.4.0"
  },
  "main": "index.html",
  "scripts": {
    "start": "nwbuild -r ."
  },
  "dependencies": {
    "serialport": "^1.4.6"
  }
}