install_ready_callback.js

<script>
  function messengerReady() {
    // Wait until the messenger is fully
    // ready, then send a message
    FxoMessenger.on('stateChanged', function(state) {
      if (state === 'connected') {
        FxoMessenger.sendMessage('Hey!');
      }
    });

    // Subscribe to all messages received,
    // logging them to the console
    FxoMessenger.on('messageReceived', function(message) {
      console.log(message);
    });
  }
</script>
<script src="https://widget.flowxo.com/embed.js?callback=messengerReady" async defer data-fxo-widget="my-own-widget-code"></script>

I think if you change this to an HTML file you'll get nicer highlighting?