WebSocket: bufferedAmount property
Baseline Widely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
The WebSocket.bufferedAmount read-only property returns
the number of bytes of data that have been queued using calls to send() but
not yet transmitted to the network. This value resets to zero once all queued data has
been sent. This value does not reset to zero when the connection is closed; if you keep
calling About