url

The URL of the target WebSocket server to connect to.The URL must use one of the following schemes:ws,wss,http, orhttps, and cannot include aURL fragment.If a relative URL is provided, it is relative to the base URL of the calling script.

protocolsOptional

A single string or an array of strings representing thesub-protocol(s) that the client would like to use, in order of preference.If it is omitted, an empty array is used by default, i.e.,[].

A single server can implement multiple WebSocket sub-protocols, and handle different types of interactions depending on the specified value.Note however that only one sub-protocol can be selected per connection.

The allowed values are those that can be specified in theSec-WebSocket-Protocol HTTP header.These are values selected from theIANA WebSocket Subprotocol Name Registry, such assoap,wamp,ship and so on, or may be a custom name jointly understood by the client and the server.

Note:The connection is not established until the sub-protocol is negotiated with the server.The selected protocol can then be read fromWebSocket.protocol: it will be the empty string if a connection cannot be established.

SyntaxErrorDOMException

Thrown if:

• parsing ofurl fails
• url has a scheme other thanws,wss,http, orhttps
• url has afragment
• any of the values inprotocols occur more than once, or otherwise fail to match the requirements for elements that comprise the value ofSec-WebSocket-Protocol fields as defined by the WebSocket Protocol specification

The examples below show how you might connect to aWebSocket.

The code below shows how we can connect to a socket using an URL with thewss schema:

const wssWebSocket = new WebSocket("wss://websocket.example.org");console.log(wssWebSocket.url); // 'wss://websocket.example.org'// Do something with socketwssWebSocket.close();

The code for connecting to an HTTPS URL is nearly the same.Under the hood the browser resolves this to a "WSS" connection, so theWebSocket.url will have the schema "wss:".

const httpsWebSocket = new WebSocket("https://websocket.example.org");console.log(httpsWebSocket.url); // 'wss://websocket.example.org'// Do something with sockethttpsWebSocket.close();

We can also resolve relative URLs.The absolute URL will depend on the base URL of the context in which it is called.

relativeWebSocket = new WebSocket("/local/url");// Do something with socketrelativeWebSocket.close();

• RFC 6455 (the WebSocket Protocol specification)