Reserved. Used to indicate that a connection was closed abnormally (that is, with no close frame being sent) when a status code is expected.

The server was acting as a gateway or proxy and received an invalid response from the upstream server. This is similar to 502 HTTP Status Code.

The endpoint is going away, either because of a server failure or because the browser is navigating away from the page that opened the connection.

The server is terminating the connection because it encountered an unexpected condition that prevented it from fulfilling the request.

The endpoint is terminating the connection because a message was received that contained inconsistent data (e.g., non-UTF-8 data within a text message).

The endpoint is terminating the connection because a data frame was received that is too large.

The client is terminating the connection because it expected the server to negotiate one or more extension, but the server didn't.

Reserved. Indicates that no status code was provided even though one was expected.

Normal closure; the connection successfully completed whatever purpose for which it was created.

The endpoint is terminating the connection because it received a message that violates its policy. This is a generic status code, used when codes 1003 and 1009 are not suitable.

The endpoint is terminating the connection due to a protocol error.

The server is terminating the connection because it is restarting. [Ref]

Reserved. Indicates that the connection was closed due to a failure to perform a TLS handshake (e.g., the server certificate can't be verified).

The server is terminating the connection due to a temporary condition, e.g. it is overloaded and is casting off some of its clients. [Ref]

The connection is being terminated because the endpoint received data of a type it cannot accept (for example, a text-only endpoint received binary data).