Intercept HTTP errors in SignalR JavaScript Client

This is more of a question then a issue.
I'm using the @microsoft/signalr (v.6.0.0) javascript client in my Vue project.
This is my Connection Builder

`client = new HubConnectionBuilder()
.withUrl('/chat', { accessTokenFactory: () => IdService.getToken() })
.configureLogging(LogLevel.None)
.withAutomaticReconnect()
.build()`

Later when I start the connection:
`client.start().then(() => {
console.log('Connected')
}).catch((err) => {
console.error(err)
})`

What I would like to do is, if there is a error in the moment of starting the connection, I would like to know the HTTP status code from the catched error. Like this:
`client.start().then(() => {
console.log('Connected')
}).catch((err) => {
console.error(err.response.status)
})`

The problem is, the error that is getting catched is only a string. Of course I could filter the status code from the string but that seems wrong.
So my question is, is there any way or method to get the error codes?