EspruinoWifi connected / disconnected event

I'm afraid there aren't any events at the moment - where did you find out about them from? You could try this and see if it gives you what you need:

wifi.at.registerLine("WIFI CONNECTED", function() { wifi.emit("connected"); }); 
wifi.at.registerLine("WIFI DISCONNECT", function() { wifi.emit("disconnected"); }); 

I'm afraid I don't have time to test at the moment, but if it doesn't break anything else I can add it to the module. You might need to use "WIFI GOT IP" instead of "WIFI CONNECTED" though - since I guess you care more about whether you have an IP address than if you're connected.