A CloseEvent is sent to clients using WebSockets when the connection is closed. This is delivered to the listener indicated by the WebSocket object's onclose attribute.


Creates a new CloseEvent.


This interface also inherits properties from its parent, Event.

CloseEvent.code Read only
Returns an unsigned short containing the close code sent by the server. The following values are permitted status codes. The following definitions are sourced from the IANA website [Ref]. Note that the 1xxx codes are only WebSocket-internal and not for the same meaning by the transported data (like when the application-layer protocol is invalid). The only permitted codes to be specified in Firefox are 1000 and 3000 to 4999 [Source, Bug].
Status code Name Description
0999 Reserved and not used.
1000 Normal Closure Normal closure; the connection successfully completed whatever purpose for which it was created.
1001 Going Away 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.
1002 Protocol Error The endpoint is terminating the connection due to a protocol error.
1003 Unsupported Data 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).
1004 Reserved. A meaning might be defined in the future.
1005 No Status Received Reserved.  Indicates that no status code was provided even though one was expected.
1006 Abnormal Closure Reserved. Used to indicate that a connection was closed abnormally (that is, with no close frame being sent) when a status code is expected.
1007 Invalid frame payload data 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).
1008 Policy Violation 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.
1009 Message too big The endpoint is terminating the connection because a data frame was received that is too large.
1010 Missing Extension The client is terminating the connection because it expected the server to negotiate one or more extension, but the server didn't.
1011 Internal Error The server is terminating the connection because it encountered an unexpected condition that prevented it from fulfilling the request.
1012 Service Restart The server is terminating the connection because it is restarting. [Ref]
1013 Try Again Later 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]
1014 Bad Gateway 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.
1015 TLS Handshake 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).
10161999 Reserved for future use by the WebSocket standard.
20002999 Reserved for use by WebSocket extensions.
30003999 Available for use by libraries and frameworks. May not be used by applications. Available for registration at the IANA via first-come, first-serve.
40004999 Available for use by applications.
CloseEvent.reason Read only
Returns a DOMString indicating the reason the server closed the connection. This is specific to the particular server and sub-protocol.
CloseEvent.wasClean Read only
Returns a boolean value that Indicates whether or not the connection was cleanly closed.


This interface also inherits methods from its parent, Event.

Initializes the value of a CloseEvent created. If the event has already being dispatched, this method does nothing. Do not use this method anymore, use the CloseEvent() constructor instead.


HTML Standard (HTML)
# the-closeevent-interface

Browser compatibility

BCD tables only load in the browser

See also