SignalR: detect connection state on client

The client is always trying to connect. You don't need to worry about that. There's a reconnected event that you can listen to, in case you want to do something when the connection is successfully reestablished.

EDIT: This changed, the client only tries to reconnect during a certain period of time. After that, you have to catch the disconnection event and manually restart.

This answer is specific to "SignalR version 2" the latest version "ASP.NET Core SignalR" may differ.

SignalR version 2: The JS client attempts to reconnect for a certain time period, which defaults to 110 seconds. You can subscribe to the connection.stateChanged event, and get updates on when the state changes so that you can display it to the user, or validate SignalR's response to different disconnection scenarios.

In my testing, the state was correctly updated to disconnected and reconnecting etc., as you would expect.

More information on signalr connections

function connectionStateChanged(state) {
    var stateConversion = {0: 'connecting', 1: 'connected', 2: 'reconnecting', 4: 'disconnected'};
    console.log('SignalR state changed from: ' + stateConversion[state.oldState]
     + ' to: ' + stateConversion[state.newState]);
}

connection = $.connection(signalR_Endpoint);
connection.stateChanged(connectionStateChanged);
connection.start({ waitForPageLoad: false });