Get SignalrR ConnectionId on ClientSide (Angular App)

From Javascript... Just interrogate the connection id property of the SignalR connection once a connection is made (in the start().done function). Like this:

var connectionid = _signalconnection.connection.connectionId;

Just be sure to do this in both the start().done and the onreconnected event. That allows you to get the updated connectionid if it changes on a reconnect.

Pretty straightforward.

Here's my connection start statement, in case it helps...

    _signalconnection.start().then(function ()
    {
        console.log("Setup_SignalR: connection open.");
        
        // Get the connectionID...
        _connectionid = _signalconnection.connection.connectionId;
        
        // Make a log entry that is page contextual...
        var page = window.location.pathname;
        console.log("Setup_SignalR:ConnectionOpen for page (" + page + ") with connectionID = " + _connectionid);
        
    }).catch(function (err)
    {
        console.error("Setup_SignalR: connection failed. err = " + err);
    });

Client:

let connection: signalR.HubConnection;
let accessToken = "3076a225-f2f6-4c68-b894-08accb62bb90";

connection = new signalR.HubConnectionBuilder().withUrl("http://localhost:8178/notifyHub", { accessTokenFactory: () => accessToken }).build();
connection.start().then(function(){connection.invoke("GetConnectionId").then(function(connectionId){console.log(connectionId)})}).catch(err => console.error(err));

Seems like an XY problem.

Tell all other clients (problem X)

Hub:

public async Task TellAllOtherClients(object[] args)
{
    await Clients.Others.SendAsync("method", args);
}

Get connectionId (solution Y)

Hub:

public string GetConnectionId()
{
    return Context.ConnectionId;
}

Client:

hub.invoke('getConnectionId')
    .then(function (connectionId) {
        // Send the connectionId to controller
    });