CYJS automatically detects if you’re loosing network with a keepalive checking. An alert message will be displayed and that network icon will blink many times to finally get less opaque.
When network will come back, you’ll get another alert and that icon will get its normal opacity back.
That keepalive is done on CYJS/js/keepalive file, usually empty. That means the network check is made from your own computer to your webapp server, so if your server would loose connection, your app would also loose network however you can have Internet access.