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WebSocket Events

The API for WebSocket is based around events.

WebSocket fires four events, which are available from the JavaScript API and defined by the W3C:

  • open
  • message
  • error
  • close

With JavaScript, you listen for these events to fire either with the handler on<eventname>, or the addEventListener() method. Your code will provide a callback that will execute every time that event gets fired.

Breakdown of the Table

Event Handler Event Type
onopen open
onmessage message
onerror error
onclose close

Each event handler is a property on the WebSocket object that lets you define a function to run when that event occurs.

BOOK

WebSocket Methods

The creators of WebSocket kept its methods pretty simple. There are only two:

  1. send() &
  2. close().

Method: Send

Method: Close

BOOK

WebSocket Attributes

When the event for open is fired, the WebSocket object can have several possible attributes that can be read in your client applications.

Attribute: readyState

Attribute: bufferedAmount

Attribute: protocol

Testing for WebSocket Support

For now, here is a quick way to check whether the API is supported on the client:

if (window.WebSocket) {
  console.log("WebSocket: supported");
  // ... code here for doing WebSocket stuff
} else {
  console.log("WebSocket: unsupported");
  // ... fallback mode, or error back to user
}

Reference

Books

WebSocket by Andrew Lombardi