How to set connection id in SignalR client?

I need to set connection id before hubConnection.start(); I look here https://github.com/SignalR/SignalR/wiki/SignalR-JS-Client and what i found: connection.id - Gets or sets the client id for the current connection. Tried this. No working. Here is the client code:

let hubUrl = 'http://localhost:5000/chat';
let hubConnection = new signalR.HubConnectionBuilder()
        .withUrl(hubUrl)
    .configureLogging(signalR.LogLevel.Information)
    .build();
hubConnection.id = "12345";
hubConnection.on("Send", function (data) {
    let elem = document.createElement("p");
    elem.appendChild(document.createTextNode(data));
    let firstElem = document.getElementById("chatroom").firstChild;
    document.getElementById("chatroom").insertBefore(elem, firstElem);

});

document.getElementById("sendBtn").addEventListener("click", function (e) {
    let message = document.getElementById("message").value;
    hubConnection.invoke("Send", message);
});

hubConnection.start();

hubConnection.id = "12345"; this do not change real connection id. And maybe you are know some other way how to write client-side connection?