WebSocket

This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for the proper prefixes to use in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the spec changes.

The WebSocket object provides the API for creating and managing a WebSocket connection to a server, as well as for sending and receiving data on the connection.

Method overview

void close(in optional unsigned long code, in optional DOMString reason);
void send(in DOMString data);

Attributes

Attribute Type Description
binaryType DOMString A string indicating the type of binary data being transmitted by the connection. This should be either "blob" if DOM Blob objects are being used or "arraybuffer" if ArrayBuffer objects are being used.
bufferedAmount unsigned long The number of bytes of data that have been queued using calls to send() but not yet transmitted to the network. This value does not reset to zero when the connection is closed; if you keep calling send(), this will continue to climb. Read only.
extensions DOMString The extensions selected by the server. This is currently only the empty string or a list of extensions as negotiated by the connection.
onclose EventListener An event listener to be called when the WebSocket connection's readyState changes to CLOSED. The listener receives a CloseEvent named "close".
onerror EventListener An event listener to be called when an error occurs. This is a simple event named "error".
onmessage EventListener An event listener to be called when a message is received from the server. The listener receives a MessageEvent named "message".
onopen EventListener An event listener to be called when the WebSocket connection's readyState changes to OPEN; this indicates that the connection is ready to send and receive data. The event is a simple one with the name "open".
protocol DOMString A string indicating the name of the sub-protocol the server selected; this will be one of the strings specified in the protocols parameter when creating the WebSocket object.
readyState unsigned short The current state of the connection; this is one of the Ready state constants. Read only.
url DOMString The URL as resolved by the constructor. This is always an absolute URL. Read only.

Constants

Ready state constants

These constants are used by the readyState attribute to describe the state of the WebSocket connection.

Constant Value Description
CONNECTING 0 The connection is not yet open.
OPEN 1 The connection is open and ready to communicate.
CLOSING 2 The connection is in the process of closing.
CLOSED 3 The connection is closed or couldn't be opened.

Methods

close()

Closes the WebSocket connection or connection attempt, if any. If the connection is already CLOSED, this method does nothing.

void close(
  in optional unsigned short code,
  in optional DOMString reason
);
Parameters
code Optional
A numeric value indicating the status code explaining why the connection is being closed. If this parameter is not specified, a default value of 1000 (indicating a normal "transaction complete" closure) is assumed. See the list of status codes on the CloseEvent page for permitted values.
reason Optional
A human-readable string explaining why the connection is closing. This string must be no longer than 123 bytes of UTF-8 text (not characters).
Exceptions thrown
INVALID_ACCESS_ERR
An invalid code was specified.
SYNTAX_ERR
The reason string is too long or contains unpaired surrogates.
Notes

In Gecko, this method didn't support any parameters prior to Gecko 8.0 (Firefox 8.0 / Thunderbird 8.0 / SeaMonkey 2.5).

send()

Transmits data to the server over the WebSocket connection.

void send(
  in DOMString data
);

void send(
  in ArrayBuffer data
);

void send(
  in Blob data
);
Parameters
data
A text string to send to the server.
Exceptions thrown
INVALID_STATE_ERR
The connection is not currently OPEN.
SYNTAX_ERR
The data is a string that has unpaired surrogates.
Remarks

Note: Gecko's implementation of the send() method differs somewhat from the specification in Gecko 6.0; Gecko returns a boolean indicating whether or not the connection is still open (and, by extension, that the data was successfully queued or transmitted); this is corrected in Gecko 8.0.

As of Gecko 11.0, support for ArrayBuffer is implemented but not Blob data types.

See also

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support ? 4.0 (2.0) ? ? ?
Sub-protocol support ? 6.0 (6.0) ? ? ?
Feature Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support ? 7.0 (7.0) ? ? ?
Sub-protocol support ? 7.0 (7.0) ? ? ?

Gecko notes

Starting in Gecko 6.0, the constructor is prefixed; you will need to use MozWebSocket():

var mySocket = new MozWebSocket("http://www.example.com/socketserver");

The extensions attribute was not supported in Gecko until Gecko 8.0.

Note: Prior to Gecko 11.0, outbound messages sent using the send() method were limited to 16 MB. They can now be up to 2 GB in size.

Document Tags and Contributors

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Contributors to this page: evilpie, Sheppy, ericz, kscarfone, Kennyluck, teoli, Reachmeatshivam
Last updated by: kscarfone,