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Features

Custom transport implementations

The transports option now accepts an array of transport implementations:

import { io } from "socket.io-client";
import { XHR, WebSocket } from "engine.io-client";

const socket = io({
  transports: [XHR, WebSocket]
});

Here is the list of provided implementations:

Transport	Description
Fetch	HTTP long-polling based on the built-in fetch() method.
NodeXHR	HTTP long-polling based on the XMLHttpRequest object provided by the xmlhttprequest-ssl package.
XHR	HTTP long-polling based on the built-in XMLHttpRequest object.
NodeWebSocket	WebSocket transport based on the WebSocket object provided by the ws package.
WebSocket	WebSocket transport based on the built-in WebSocket object.
WebTransport	WebTransport transport based on the built-in WebTransport object.

Usage:

Transport	browser	Node.js	Deno	Bun
Fetch	✅	✅ (1)	✅	✅
NodeXHR		✅	✅	✅
XHR	✅
NodeWebSocket		✅	✅	✅
WebSocket	✅	✅ (2)	✅	✅
WebTransport	✅	✅

(1) since v18.0.0
(2) since v21.0.0

Added in f4d898e and b11763b.

Test each low-level transports

When setting the tryAllTransports option to true, if the first transport (usually, HTTP long-polling) fails, then the other transports will be tested too:

import { io } from "socket.io-client";

const socket = io({
  tryAllTransports: true
});

This feature is useful in two cases:

• when HTTP long-polling is disabled on the server, or if CORS fails
• when WebSocket is tested first (with transports: ["websocket", "polling"])

The only potential downside is that the connection attempt could take more time in case of failure, as there have been reports of WebSocket connection errors taking several seconds before being detected (that's one reason for using HTTP long-polling first). That's why the option defaults to false for now.

Added in 579b243.

Bug Fixes

• accept string | undefined as init argument (bis) (60c757f)
• allow to manually stop the reconnection loop (13c6d2e)
• close the engine upon decoding exception (04c8dd9)
• do not send a packet on an expired connection (#5134) (8adcfbf)

Dependencies

• engine.io-client@~6.6.1 (diff and diff)
• ws@~8.17.1 (diff)