4.6.0

Bug Fixes

• typings: do not expose browser-specific types (4d6d95e)
• ensure manager.socket() returns an active socket (b7dd891)
• typings: properly type emits with timeout (#1570) (33e4172)

Features

A new "addTrailingSlash" option

The trailing slash which was added by default can now be disabled:

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

const socket = io("https://example.com", {
  addTrailingSlash: false
});

In the example above, the request URL will be https://example.com/socket.io instead of https://example.com/socket.io/.

Added in 21a6e12.

Promise-based acknowledgements

This commit adds some syntactic sugar around acknowledgements:

// without timeout
const response = await socket.emitWithAck("hello", "world");

// with a specific timeout
try {
  const response = await socket.timeout(1000).emitWithAck("hello", "world");
} catch (err) {
  // the server did not acknowledge the event in the given delay
}

Note: environments that do not support Promises will need to add a polyfill in order to use this feature.

Added in 47b979d.

Connection state recovery

This feature allows a client to reconnect after a temporary disconnection and restore its ID and receive any packets that was missed during the disconnection gap. It must be enabled on the server side.

A new boolean attribute named recovered is added on the socket object:

socket.on("connect", () => {
  console.log(socket.recovered); // whether the recovery was successful
});

Added in 54d5ee0 (server) and b4e20c5 (client).

Retry mechanism

Two new options are available:

• retries: the maximum number of retries. Above the limit, the packet will be discarded.
• ackTimeout: the default timeout in milliseconds used when waiting for an acknowledgement (not to be mixed up with the already existing timeout option, which is used by the Manager during the connection)

const socket = io({
  retries: 3,
  ackTimeout: 10000
});

// implicit ack
socket.emit("my-event");

// explicit ack
socket.emit("my-event", (err, val) => { /* ... */ });

// custom timeout (in that case the ackTimeout is optional)
socket.timeout(5000).emit("my-event", (err, val) => { /* ... */ });

In all examples above, "my-event" will be sent up to 4 times (1 + 3), until the server sends an acknowledgement.

Assigning a unique ID to each packet is the duty of the user, in order to allow deduplication on the server side.

Added in 655dce9.

Links

• Diff: 4.5.4...4.6.0
• Server release: 4.6.0
• engine.io-client version: ~6.4.0 (diff)
• ws version: ~8.11.0 (diff)

Size of the bundles:

	min	min+gzip
socket.io.min.js	45.8 KB (+ 3.2 KB ⬆️)	14.5 KB (+ 0.9 KB ⬆️)
socket.io.msgpack.min.js	50.7 KB (+ 3.0 KB ⬆️)	15.5 KB (+ 0.9 KB ⬆️)
socket.io.esm.min.js	37.0 KB (+ 2.5 KB ⬆️)	12.3 KB (+ 0.8 KB ⬆️)