WebSocket: close() method

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.close() method closes the WebSocket connection or connection attempt, if any. If the connection is already CLOSED, this method does nothing.

Note: The process of closing the connection begins with a closing handshake, and the close() method does not discard previously-sent messages before starting that closing handshake; even if the user agent is still busy sending those messages, the handshake will only start after the messages are sent.

Syntax

close()
close(code)
close(code, reason)

Parameters

code Optional

An integer WebSocket connection close code value indicating a reason for closure:

If unspecified, a close code for the connection is automatically set: to 1000 for a normal closure, or otherwise to another standard value in the range 1001-1015 that indicates the actual reason the connection was closed.
If specified, the value of this code parameter overrides the automatic setting of the close code for the connection, and instead sets a custom code. The value must be an integer: either 1000, or else a custom code of your choosing in the range 3000-4999. If you specify a code value, you should also specify a reason value.

reason Optional

A string providing a custom WebSocket connection close reason (a concise human-readable prose explanation for the closure). The value must be no longer than 123 bytes (encoded in UTF-8).

Note: Because UTF-8 uses two to four bytes to encode any non-ASCII characters, a 123-character reason value containing non-ASCII characters would exceed the 123-byte limit.

If you specify a reason value, you should also specify a code value.

Return value

None (undefined).

Exceptions

InvalidAccessError DOMException: Thrown if code is neither an integer equal to 1000 nor an integer in the range 3000 – 4999.
SyntaxError DOMException: Thrown if the UTF-8-encoded reason value is longer than 123 bytes.

Specifications

Specification
WebSockets Standard # ref-for-dom-websocket-close①

Browser compatibility

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