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 1005 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()

Enqueues the specified data to be transmitted to the server over the WebSocket connection, increasing the value of bufferedAmount by the number of bytes needed to contain the data. If the data can't be sent (for example, because it needs to be buffered but the buffer is full), the socket is closed automatically.

void send(
  in USVString data
);

void send(
  in ArrayBuffer data
);

void send(
  in Blob data
);

void send(
  in ArrayBufferView data
);

Parameters

data

The data to send to the server. It may be one of the following types:

USVString

A text string. The string is added to the buffer in UTF-8 format, and the value of bufferedAmount is increased by the number of bytes required to represent the UTF-8 string.

ArrayBuffer

You can send the underlying binary data used by a typed array object; its binary data contents are queued in the buffer, increasing the value of bufferedAmount by the requisite number of bytes.

Blob

Specifying a Blob enqueues the blob's raw data to be transmitted in a binary frame. The value of bufferedAmount is increased by the byte size of that raw data.

ArrayBufferView

You can send any JavaScript typed array object as a binary frame; its binary data contents are queued in the buffer, increasing the value of bufferedAmount by the requisite number of bytes.

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