So I finally got this to work. To play videos from youtube use the following. Replace XX with your Chromecast IP and change v=XXXXXX to the video you want
executeCommandLine('curl -H “Content-Type:application/json” "http://192.168.XX.XX:8008/apps/YouTube" -X POST -d "v=dQw4w9WgXcQ"', 5000)