index.md

---
title: WebSocket
slug: Web/API/WebSocket
page-type: web-api-interface
browser-compat: api.WebSocket
---

{{APIRef("WebSockets API")}}{{AvailableInWorkers}}

The `WebSocket` object provides the API for creating and managing a [WebSocket](/en-US/docs/Web/API/WebSockets_API) connection to a server, as well as for sending and receiving data on the connection.

To construct a `WebSocket`, use the [`WebSocket()`](/en-US/docs/Web/API/WebSocket/WebSocket) constructor.

> [!NOTE]
> The `WebSocket` API has no way to apply [backpressure](/en-US/docs/Web/API/Streams_API/Concepts#backpressure), therefore when messages arrive faster than the application can process them, the application will either fill up the device's memory by buffering those messages, become unresponsive due to 100% CPU usage, or both. For an alternative that provides backpressure automatically, see {{domxref("WebSocketStream")}}.

{{InheritanceDiagram}}

## Constructor

- {{domxref("WebSocket.WebSocket", "WebSocket()")}}
  - : Returns a newly created `WebSocket` object.

## Instance properties

- {{domxref("WebSocket.binaryType")}}
  - : The binary data type used by the connection.
- {{domxref("WebSocket.bufferedAmount")}} {{ReadOnlyInline}}
  - : The number of bytes of queued data.
- {{domxref("WebSocket.extensions")}} {{ReadOnlyInline}}
  - : The extensions selected by the server.
- {{domxref("WebSocket.protocol")}} {{ReadOnlyInline}}
  - : The sub-protocol selected by the server.
- {{domxref("WebSocket.readyState")}} {{ReadOnlyInline}}
  - : The current state of the connection.
- {{domxref("WebSocket.url")}} {{ReadOnlyInline}}
  - : The absolute URL of the WebSocket.

## Instance methods

- {{domxref("WebSocket.close()")}}
  - : Closes the connection.
- {{domxref("WebSocket.send()")}}
  - : Enqueues data to be transmitted.

## Events

Listen to these events using `addEventListener()` or by assigning an event listener to the `oneventname` property of this interface.

- {{domxref("WebSocket/close_event", "close")}}
  - : Fired when a connection with a `WebSocket` is closed.
    Also available via the `onclose` property
- {{domxref("WebSocket/error_event", "error")}}
  - : Fired when a connection with a `WebSocket` has been closed because of an error, such as when some data couldn't be sent.
    Also available via the `onerror` property.
- {{domxref("WebSocket/message_event", "message")}}
  - : Fired when data is received through a `WebSocket`.
    Also available via the `onmessage` property.
- {{domxref("WebSocket/open_event", "open")}}
  - : Fired when a connection with a `WebSocket` is opened.
    Also available via the `onopen` property.

## Examples

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

// Connection opened
socket.addEventListener("open", (event) => {
  socket.send("Hello Server!");
});

// Listen for messages
socket.addEventListener("message", (event) => {
  console.log("Message from server ", event.data);
});
```

## Specifications

{{Specifications}}

## Browser compatibility

{{Compat}}

## See also

- [Writing WebSocket client applications](/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_client_applications)