EventSource interface is used to receive server-sent events. It connects to a server over HTTP and receives events in
text/event-stream format without closing the connection.
EventHandler being called when an error occurs and the
error event is dispatched on this object.
EventHandler being called when a
message event is received, that is when a message is coming from the source.
EventHandler being called when an
open event is received, that is when the connection was just opened.
unsigned short representing the state of the connection. Possible values are