WebSocket

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.

The WebSocket constructor accepts one required and one optional parameter:

WebSocket WebSocket(
  in DOMString url,
  in optional DOMString protocols
);

WebSocket WebSocket(
  in DOMString url,
  in optional DOMString[] protocols
);

url

The URL to which to connect; this should be the URL to which the WebSocket server will respond.

protocols Optional

Either a single protocol string or an array of protocol strings. These strings are used to indicate sub-protocols, so that a single server can implement multiple WebSocket sub-protocols (for example, you might want one server to be able to handle different types of interactions depending on the specified protocol). If you don't specify a protocol string, an empty string is assumed.

The constructor can throw exceptions:

SECURITY_ERR

The port to which the connection is being attempted is being blocked.

Method overview

Attributes

Constants

Ready state constants

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

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.

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.

Example

// Create WebSocket connection.
const socket = new WebSocket('ws://localhost:8080');

// Connection opened
socket.addEventListener('open', function (event) {
    socket.send('Hello Server!');
});

// Listen for messages
socket.addEventListener('message', function (event) {
    console.log('Message from server', event.data);
});

Specifications

Browser compatibility

[1] Starting in Gecko 6.0 (Firefox 6.0 / Thunderbird 6.0 / SeaMonkey 2.3), 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.

Prior to Gecko 11.0 (Firefox 11.0 / Thunderbird 11.0 / SeaMonkey 2.8), outbound messages sent using the send() method were limited to 16 MB. They can now be up to 2 GB in size.

See also

• Writing WebSocket client applications