# Changelog

| Version                                                                                                     | Release date   | Bundle size (UMD min+gzip) |
|-------------------------------------------------------------------------------------------------------------|----------------|----------------------------|
| [4.8.2](#482-2025-12-22)                                                                                    | December 2024  | `14.4 KB`                  |
| [4.8.1](#481-2024-10-25)                                                                                    | October 2024   | `14.4 KB`                  |
| [4.8.0](#480-2024-09-21)                                                                                    | September 2024 | `14.4 KB`                  |
| [4.7.5](#475-2024-03-14)                                                                                    | March 2024     | `14.6 KB`                  |
| [4.7.4](#474-2024-01-12)                                                                                    | January 2024   | `14.5 KB`                  |
| [4.7.3](#473-2024-01-03)                                                                                    | January 2024   | `14.5 KB`                  |
| [4.7.2](#472-2023-08-02)                                                                                    | August 2023    | `14.5 KB`                  |
| [4.7.1](#471-2023-06-28)                                                                                    | June 2023      | `14.1 KB`                  |
| [4.7.0](#470-2023-06-22)                                                                                    | June 2023      | `14.0 KB`                  |
| [4.6.2](#462-2023-05-31)                                                                                    | May 2023       | `13.4 KB`                  |
| [4.6.1](#461-2023-02-20)                                                                                    | February 2023  | `13.3 KB`                  |
| [4.6.0](#460-2023-02-07)                                                                                    | February 2023  | `13.3 KB`                  |
| [4.5.4](#454-2022-11-22)                                                                                    | November 2022  | `12.8 KB`                  |
| [4.5.3](#453-2022-10-15)                                                                                    | October 2022   | `12.8 KB`                  |
| [4.5.2](#452-2022-09-02)                                                                                    | September 2022 | `12.7 KB`                  |
| [2.5.0](#250-2022-06-26) (from the [2.x](https://github.com/socketio/socket.io-client/tree/2.x) branch)     | June 2022      | `18.8 KB`                  |
| [4.5.1](#451-2022-05-17)                                                                                    | May 2022       | `12.7 KB`                  |
| [4.5.0](#450-2022-04-23)                                                                                    | April 2022     | `12.7 KB`                  |
| [4.4.1](#441-2022-01-06)                                                                                    | January 2022   | `12.3 KB`                  |
| [4.4.0](#440-2021-11-18)                                                                                    | November 2021  | `12.3 KB`                  |
| [4.3.2](#432-2021-10-16)                                                                                    | October 2021   | `12.1 KB`                  |
| [4.3.1](#431-2021-10-15)                                                                                    | October 2021   | `12.1 KB`                  |
| [4.3.0](#430-2021-10-14)                                                                                    | October 2021   | `12.1 KB`                  |
| [4.2.0](#420-2021-08-30)                                                                                    | August 2021    | `15.2 KB`                  |
| [4.1.3](#413-2021-07-10)                                                                                    | July 2021      | `14.9 KB`                  |
| [4.1.2](#412-2021-05-17)                                                                                    | May 2021       | `14.9 KB`                  |
| [4.1.1](#411-2021-05-11)                                                                                    | May 2021       | `14.9 KB`                  |
| [4.1.0](#410-2021-05-11)                                                                                    | May 2021       | `14.9 KB`                  |
| [4.0.2](#402-2021-05-06)                                                                                    | May 2021       | `14.9 KB`                  |
| [4.0.1](#401-2021-03-31)                                                                                    | March 2021     | `14.9 KB`                  |
| [3.1.3](#313-2021-03-12) (from the [3.1.x](https://github.com/socketio/socket.io-client/tree/3.1.x) branch) | March 2021     | `14.6 KB`                  |
| [**4.0.0**](#400-2021-03-10)                                                                                | March 2021     | `14.9 KB`                  |
| [3.1.2](#312-2021-02-26)                                                                                    | February 2021  | `14.6 KB`                  |
| [3.1.1](#311-2021-02-03)                                                                                    | February 2021  | `14.5 KB`                  |
| [3.1.0](#310-2021-01-15)                                                                                    | January 2021   | `14.5 KB`                  |
| [3.0.5](#305-2021-01-05)                                                                                    | January 2021   | `14.5 KB`                  |
| [2.4.0](#240-2021-01-04) (from the [2.x](https://github.com/socketio/socket.io-client/tree/2.x) branch)     | January 2021   | `18.8 KB`                  |
| [3.0.4](#304-2020-12-07)                                                                                    | December 2020  | `14.6 KB`                  |
| [3.0.3](#303-2020-11-19)                                                                                    | November 2020  | `14.5 KB`                  |
| [3.0.2](#302-2020-11-17)                                                                                    | November 2020  | `14.5 KB`                  |
| [3.0.1](#301-2020-11-09)                                                                                    | November 2020  | `14.7 KB`                  |
| [**3.0.0**](#300-2020-11-05)                                                                                | November 2020  | `14.6 KB`                  |
| [2.3.1](#231-2020-09-30)                                                                                    | September 2020 | `18.8 KB`                  |
| [2.3.0](#230-2019-09-20)                                                                                    | September 2019 | `19.6 KB`                  |
| [2.2.0](#220-2018-11-29)                                                                                    | November 2018  | `18.6 KB`                  |
| [2.1.1](#211-2018-05-17)                                                                                    | May 2018       | `18.7 KB`                  |
| [2.1.0](#210-2018-03-29)                                                                                    | March 2018     | `18.7 KB`                  |


## [4.8.2](https://github.com/socketio/socket.io/compare/socket.io-client@4.8.1...socket.io-client@4.8.2) (2025-12-22)


### Bug Fixes

* **bundle** do not mangle the "_placeholder" attribute (bis) ([cdae019](https://github.com/socketio/socket.io/commit/cdae01983a8ae840fc9812875a8b88166b377c11))
* drain queue before emitting "connect" ([#5259](https://github.com/socketio/socket.io/issues/5259)) ([d19928e](https://github.com/socketio/socket.io/commit/d19928e8d8b325310274031ed7de2ddc93ebb589)


### Dependencies

- [`engine.io-client@~6.6.1`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) (no change)
- [`ws@~8.17.1`](https://github.com/websockets/ws/releases/tag/8.17.1) (no change)



## [4.8.1](https://github.com/socketio/socket.io/compare/socket.io-client@4.8.0...socket.io-client@4.8.1) (2024-10-25)


### Bug Fixes

* **bundle:** do not mangle the "_placeholder" attribute ([ca9e994](https://github.com/socketio/socket.io/commit/ca9e994815aa2e31e0342e37ccdc2e9e8c5fd13c))


### Dependencies

- [`engine.io-client@~6.6.1`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) (no change)
- [`ws@~8.17.1`](https://github.com/websockets/ws/releases/tag/8.17.1) (no change)



## [4.8.0](https://github.com/socketio/socket.io/compare/socket.io-client@4.7.5...socket.io-client@4.8.0) (2024-09-21)

### Features

#### Custom transport implementations

The `transports` option now accepts an array of transport implementations:

```js
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`         | :white_check_mark: | :white_check_mark: (1) | :white_check_mark: | :white_check_mark: |
| `NodeXHR`       |                    | :white_check_mark:     | :white_check_mark: | :white_check_mark: |
| `XHR`           | :white_check_mark: |                        |                    |                    |
| `NodeWebSocket` |                    | :white_check_mark:     | :white_check_mark: | :white_check_mark: |
| `WebSocket`     | :white_check_mark: | :white_check_mark: (2) | :white_check_mark: | :white_check_mark: |
| `WebTransport`  | :white_check_mark: | :white_check_mark:     |                    |                    |

(1) since [v18.0.0](https://nodejs.org/api/globals.html#fetch)
(2) since [v21.0.0](https://nodejs.org/api/globals.html#websocket)

Added in [f4d898e](https://github.com/socketio/engine.io-client/commit/f4d898ee9652939a4550a41ac0e8143056154c0a) and [b11763b](https://github.com/socketio/engine.io-client/commit/b11763beecfe4622867b4dec9d1db77460733ffb).


#### 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:

```js
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](https://github.com/socketio/engine.io-client/commit/579b243e89ac7dc58233f9844ef70817364ecf52).


### Bug Fixes

* accept string | undefined as init argument (bis) ([60c757f](https://github.com/socketio/socket.io/commit/60c757f718d400e052c3160ee377bbe4973277c9))
* allow to manually stop the reconnection loop ([13c6d2e](https://github.com/socketio/socket.io/commit/13c6d2e89deb1e6c6c8c7245118f9b37d66537cb))
* close the engine upon decoding exception ([04c8dd9](https://github.com/socketio/socket.io/commit/04c8dd979ce40acaceec1f4507c1ae69325d6158))
* do not send a packet on an expired connection ([#5134](https://github.com/socketio/socket.io/issues/5134)) ([8adcfbf](https://github.com/socketio/socket.io/commit/8adcfbfde50679095ec2abe376650cf2b6814325))


### Dependencies

- [`engine.io-client@~6.6.1`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) ([diff](https://github.com/socketio/engine.io-client/compare/6.5.3...6.6.0) and [diff](https://github.com/socketio/socket.io/compare/engine.io-client@6.6.0...engine.io-client@6.6.1))
- [`ws@~8.17.1`](https://github.com/websockets/ws/releases/tag/8.17.1) ([diff](https://github.com/websockets/ws/compare/8.11.0...8.17.1))



## [4.7.5](https://github.com/socketio/socket.io-client/compare/4.7.4...4.7.5) (2024-03-14)


### Bug Fixes

* discard acknowledgements upon disconnection ([34cbfbb](https://github.com/socketio/socket.io-client/commit/34cbfbb532ae333f4dd034138e8f87cb80a8e382))


### Dependencies

- [`engine.io-client@~6.5.2`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) (no change)
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.7.4](https://github.com/socketio/socket.io-client/compare/4.7.3...4.7.4) (2024-01-12)

There were some minor bug fixes on the server side, which mandate a client bump.


### Dependencies

- [`engine.io-client@~6.5.2`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) (no change)
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.7.3](https://github.com/socketio/socket.io-client/compare/4.7.2...4.7.3) (2024-01-03)


### Bug Fixes

* improve compatibility with node16 module resolution ([#1595](https://github.com/socketio/socket.io-client/issues/1595)) ([605de78](https://github.com/socketio/socket.io-client/commit/605de78d2cd7303bf25d9e2146e2b707dbf63d4f))
* **typings:** accept string | undefined as init argument ([5a3eafe](https://github.com/socketio/socket.io-client/commit/5a3eafed1c4118ac3a06ec81a24491eec7d0655f))
* **typings:** fix the type of the socket#id attribute ([f9c16f2](https://github.com/socketio/socket.io-client/commit/f9c16f226512fc8a8df461e3a07e392720462165))


### Dependencies

- [`engine.io-client@~6.5.2`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) (no change)
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.7.2](https://github.com/socketio/socket.io-client/compare/4.7.1...4.7.2) (2023-08-02)

Some bug fixes are included from the `engine.io-client` package:

* **webtransport:** add proper framing ([d55c39e](https://github.com/socketio/engine.io-client/commit/d55c39e0ed5cb7b3a34875a398efc111c91184f6))
* **webtransport:** honor the binaryType attribute ([8270e00](https://github.com/socketio/engine.io-client/commit/8270e00d5b865278d136a4d349b344cbc2b38dc5))


### Dependencies

- [`engine.io-client@~6.5.2`](https://github.com/socketio/engine.io-client/releases/tag/6.5.2) ([diff](https://github.com/socketio/engine.io-client/compare/6.5.1...6.5.2))
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.7.1](https://github.com/socketio/socket.io-client/compare/4.7.0...4.7.1) (2023-06-28)

Some bug fixes are included from the `engine.io-client` package:

* make closeOnBeforeunload default to false ([a63066b](https://github.com/socketio/engine.io-client/commit/a63066bdc8ae9e6746c3113d06c2ead78f4a4851))
* **webtransport:** properly handle abruptly closed connections ([cf6aa1f](https://github.com/socketio/engine.io-client/commit/cf6aa1f43c27a56c076bf26fddfce74bfeb65040))


### Dependencies

- [`engine.io-client@~6.5.1`](https://github.com/socketio/engine.io-client/releases/tag/6.5.1) ([diff](https://github.com/socketio/engine.io-client/compare/6.5.0...6.5.1))
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.7.0](https://github.com/socketio/socket.io-client/compare/4.6.2...4.7.0) (2023-06-22)


### Bug Fixes

* properly report timeout error when connecting ([5bc94b5](https://github.com/socketio/socket.io-client/commit/5bc94b56bc1788bab16d9d514d2c8abf3b1d8f87))
* use same scope for setTimeout and clearTimeout calls ([#1568](https://github.com/socketio/socket.io-client/issues/1568)) ([f2892ab](https://github.com/socketio/socket.io-client/commit/f2892aba0beeae7c9be930221655d7da6094c5f1))


### Features

#### Support for WebTransport

The Engine.IO client can now use WebTransport as the underlying transport.

WebTransport is a web API that uses the HTTP/3 protocol as a bidirectional transport. It's intended for two-way communications between a web client and an HTTP/3 server.

References:

- https://w3c.github.io/webtransport/
- https://developer.mozilla.org/en-US/docs/Web/API/WebTransport
- https://developer.chrome.com/articles/webtransport/

**For Node.js clients**: until WebTransport support lands [in Node.js](https://github.com/nodejs/node/issues/38478), you can use the `@fails-components/webtransport` package:

```js
import { WebTransport } from "@fails-components/webtransport";

global.WebTransport = WebTransport;
```

Added in [7195c0f](https://github.com/socketio/engine.io-client/commit/7195c0f305b482f7b1ca2ed812030caaf72c0906).

#### Cookie management for the Node.js client

When setting the `withCredentials` option to `true`, the Node.js client will now include the cookies in the HTTP requests, making it easier to use it with cookie-based sticky sessions.

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

const socket = io("https://example.com", {
  withCredentials: true
});
```

Added in [5fc88a6](https://github.com/socketio/engine.io-client/commit/5fc88a62d4017cdc144fa39b9755deadfff2db34).

#### Conditional import of the ESM build with debug logs

By default, the ESM build does not include the `debug` package in the browser environments, because it increases the bundle size (see [16b6569](https://github.com/socketio/socket.io-client/commit/16b65698aed766e1e645c78847f2e91bfc5b6f56)).

Which means that, unfortunately, debug logs are not available in the devtools console, even when setting the `localStorage.debug = ...` attribute.

You can now import the build which includes the `debug` packages with a [conditional import](https://nodejs.org/api/packages.html#conditional-exports). Example with vite:

```js
import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'

export default defineConfig({
  plugins: [react()],
  server: {
    port: 4000
  },
  resolve: {
    conditions: ["development"]
  }
})
```

Reference: https://v2.vitejs.dev/config/#resolve-conditions

Added in [781d753](https://github.com/socketio/socket.io-client/commit/781d753a626d01e675056a2ff4e27f5dd599564f).


### Dependencies

- [`engine.io-client@~6.5.0`](https://github.com/socketio/engine.io-client/releases/tag/6.5.0) ([diff](https://github.com/socketio/engine.io-client/compare/6.4.0...6.5.0))
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.6.2](https://github.com/socketio/socket.io-client/compare/4.6.1...4.6.2) (2023-05-31)


### Bug Fixes

* **exports:** move `types` condition to the top ([#1580](https://github.com/socketio/socket.io-client/issues/1580)) ([7ead241](https://github.com/socketio/socket.io-client/commit/7ead241ecfd9f122db6789b5f2d11c04e9427953))


### Dependencies

- [`engine.io-client@~6.4.0`](https://github.com/socketio/engine.io-client/releases/tag/6.4.0) (no change)
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.6.1](https://github.com/socketio/socket.io-client/compare/4.6.0...4.6.1) (2023-02-20)


### Bug Fixes

* do not drain the queue while the socket is offline ([4996f9e](https://github.com/socketio/socket.io-client/commit/4996f9ee71074e2d62a0f8fa95fcf7d43e99615d))
* prevent duplicate connections when multiplexing ([46213a6](https://github.com/socketio/socket.io-client/commit/46213a647ea0d4453b00bca09268f69ffd259509))


### Dependencies

- [`engine.io-client@~6.4.0`](https://github.com/socketio/engine.io-client/releases/tag/6.4.0) (no change)
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) (no change)



## [4.6.0](https://github.com/socketio/socket.io-client/compare/4.5.4...4.6.0) (2023-02-07)


### Bug Fixes

* **typings:** do not expose browser-specific types ([4d6d95e](https://github.com/socketio/socket.io-client/commit/4d6d95e0792efd43b78c760b055764fef02ebc9e))
* ensure manager.socket() returns an active socket ([b7dd891](https://github.com/socketio/socket.io-client/commit/b7dd891e890461d33a104ca9187d5cd30d6f76af))
* **typings:** properly type emits with timeout ([#1570](https://github.com/socketio/socket.io-client/issues/1570)) ([33e4172](https://github.com/socketio/socket.io-client/commit/33e417258c9a5697e001163971ae87821e9c097f))


### Features

#### A new "addTrailingSlash" option

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

```js
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](https://github.com/socketio/engine.io-client/commit/21a6e1219add92157c5442537d24fbe1129a50f5).

#### Promise-based acknowledgements

This commit adds some syntactic sugar around acknowledgements:

```js
// 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](https://caniuse.com/promises) will need to add a polyfill in order to use this feature.

Added in [47b979d](https://github.com/socketio/socket.io-client/commit/47b979d57388e9b5e9a332f3f4a9873211f0d844).

#### 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:

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

Added in [54d5ee0](https://github.com/socketio/socket.io/commit/54d5ee05a684371191e207b8089f09fc24eb5107) (server) and [b4e20c5](https://github.com/socketio/socket.io-client/commit/b4e20c5c709b5e9cc03ee9b6bd1d576f4810a817) (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)

```js
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](https://github.com/socketio/socket.io-client/commit/655dce97556a1ea44a60db6b694d0cfd85b5f70f).


### Dependencies

- [`engine.io-client@~6.4.0`](https://github.com/socketio/engine.io-client/releases/tag/6.4.0) ([diff](https://github.com/socketio/engine.io-client/compare/6.2.3...6.4.0))
- [`ws@~8.11.0`](https://github.com/websockets/ws/releases/tag/8.11.0) ([diff](https://github.com/websockets/ws/compare/8.2.3...8.11.0))



## [4.5.4](https://github.com/socketio/socket.io-client/compare/4.5.3...4.5.4) (2022-11-22)

This release contains a bump of the `socket.io-parser` dependency, in order to fix [CVE-2022-2421](https://github.com/advisories/GHSA-qm95-pgcg-qqfq).

### Dependencies

- [`engine.io-client@~6.2.3`](https://github.com/socketio/engine.io-client/tree/6.2.3) (no change)
- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)



## [4.5.3](https://github.com/socketio/socket.io-client/compare/4.5.2...4.5.3) (2022-10-15)


### Bug Fixes

* do not swallow user exceptions ([2403b88](https://github.com/socketio/socket.io-client/commit/2403b88057bf3fd32eb2047c82be26c455c13a2f))

### Dependencies

- [`engine.io-client@~6.2.3`](https://github.com/socketio/engine.io-client/tree/6.2.3) (https://github.com/socketio/engine.io-client/compare/6.2.1...6.2.3)
- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)



## [4.5.2](https://github.com/socketio/socket.io-client/compare/4.5.1...4.5.2) (2022-09-02)


### Bug Fixes

* handle ill-formatted packet from server ([c597023](https://github.com/socketio/socket.io-client/commit/c5970231699aa47b00c4a617af4239d0fa90fa53))

### Dependencies

- [`engine.io-client@~6.2.1`](https://github.com/socketio/engine.io-client/releases/tag/6.2.1) (no change)
- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)



# [2.5.0](https://github.com/socketio/socket.io-client/compare/2.4.0...2.5.0) (2022-06-26)


### Bug Fixes

* ensure buffered events are sent in order ([991eb0b](https://github.com/Automattic/socket.io-client/commit/991eb0b0289bbbf680099e6d42b302beee7568b8))

### Dependencies

- [`engine.io-client@~3.5.0`](https://github.com/socketio/engine.io-client/releases/tag/3.5.0) (no change)
- [`ws@~7.4.2`](https://github.com/websockets/ws/releases/tag/7.4.2) (no change)



## [4.5.1](https://github.com/socketio/socket.io-client/compare/4.5.0...4.5.1) (2022-05-17)

There were some minor bug fixes on the server side, which mandate a client bump.

### Dependencies

- [`engine.io-client@~6.2.1`](https://github.com/socketio/engine.io-client/releases/tag/6.2.1) (no change)
- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)



# [4.5.0](https://github.com/socketio/socket.io-client/compare/4.4.1...4.5.0) (2022-04-23)


### Features

#### Additional details for the disconnect event

The "disconnect" event will now include additional details to help debugging if anything has gone wrong.

Example when a payload is over the maxHttpBufferSize value in HTTP long-polling mode:

```js
socket.on("disconnect", (reason, details) => {
  console.log(reason); // "transport error"

  // in that case, details is an error object
  console.log(details.message); "xhr post error"
  console.log(details.description); // 413 (the HTTP status of the response)

  // details.context refers to the XMLHttpRequest object
  console.log(details.context.status); // 413
  console.log(details.context.responseText); // ""
});
```

Added in [b862924](https://github.com/socketio/socket.io-client/commit/b862924b7f1720979e5db2f0154906b305d420e3).

#### Catch-all listeners for outgoing packets

This is similar to `onAny()`, but for outgoing packets.

Syntax:

```js
socket.onAnyOutgoing((event, ...args) => {
  console.log(event);
});
```

Added in [74e3e60](https://github.com/socketio/socket.io-client/commit/74e3e601a43133b2c0ea43c3de2764cc55b57b5a).

#### Slice write buffer according to the maxPayload value

The server will now include a "maxPayload" field in the handshake details, allowing the clients to decide how many packets they have to send to stay under the `maxHttpBufferSize` value.

Added in [46fdc2f](https://github.com/socketio/engine.io-client/commit/46fdc2f0ed352b454614247406689edc9d908927).

### Dependencies

- [`engine.io-client@~6.2.1`](https://github.com/socketio/engine.io-client/releases/tag/6.2.1) (https://github.com/socketio/engine.io-client/compare/6.1.1...6.2.1)
- [`ws@~8.2.3`](https://github.com/websockets/ws/releases/tag/8.2.3) (no change)



## [4.4.1](https://github.com/socketio/socket.io-client/compare/4.4.0...4.4.1) (2022-01-06)



# [4.4.0](https://github.com/socketio/socket.io-client/compare/4.3.2...4.4.0) (2021-11-18)


### Bug Fixes

* add package name in nested package.json ([53d8fca](https://github.com/socketio/socket.io-client/commit/53d8fcafabbfddb5834012c9c98743bfe6e13347)), closes [socketio/socket.io-client#1513](https://github.com/socketio/socket.io-client/issues/1513)
* fix `socket.disconnect().connect()` usage ([99c2cb8](https://github.com/socketio/socket.io-client/commit/99c2cb8421361487ed7c876edd8670bb69a5c5b5))
* prevent socket from reconnecting after middleware failure ([d54d12c](https://github.com/socketio/socket.io-client/commit/d54d12ce634193d14b71894496ed57d35d922378))


### Features

* add timeout feature ([ccf7998](https://github.com/socketio/socket.io-client/commit/ccf7998cc5049d02022567aedfb263de875a06a5))

```js
socket.timeout(5000).emit("my-event", (err) => {
  if (err) {
    // the server did not acknowledge the event in the given delay
  }
});
```



## [4.3.2](https://github.com/socketio/socket.io-client/compare/4.3.1...4.3.2) (2021-10-16)


### Bug Fixes

* restore the default export (bis) ([6780f29](https://github.com/socketio/socket.io-client/commit/6780f29624372a76aafb0bbd6975864280239f26))



## [4.3.1](https://github.com/socketio/socket.io-client/compare/4.3.0...4.3.1) (2021-10-15)


### Bug Fixes

* restore the default export ([f0aae84](https://github.com/socketio/socket.io-client/commit/f0aae8457a8bdf7e2f2286b4b7d34d2798419456))
* restore the namespace export ([8737d0a](https://github.com/socketio/socket.io-client/commit/8737d0ae6fb362455015e6dd435010c36d023663))



# [4.3.0](https://github.com/socketio/socket.io-client/compare/4.2.0...4.3.0) (2021-10-14)

An ESM bundle is now provided:

```html
<script type="module">
  import { io } from "https://cdn.socket.io/4.3.0/socket.io.esm.min.js";

  const socket = io();

  socket.emit("hello", "world");
</script>
```

### Features

* **typings:** add missing types for some emitter methods ([#1502](https://github.com/socketio/socket.io-client/issues/1502)) ([a9e5b85](https://github.com/socketio/socket.io-client/commit/a9e5b85580e8edca0b0fd2850c3741d3d86a96e2))
* provide an ESM build with and without debug ([16b6569](https://github.com/socketio/socket.io-client/commit/16b65698aed766e1e645c78847f2e91bfc5b6f56))
* migrate to rollup ([0661564](https://github.com/socketio/socket.io-client/commit/0661564dc2005b95843ddb65621b7e89af702bc0))



# [4.2.0](https://github.com/socketio/socket.io-client/compare/4.1.3...4.2.0) (2021-08-30)


### Bug Fixes

* **typings:** allow async listener in typed events ([66e00b7](https://github.com/socketio/socket.io-client/commit/66e00b7dd7c4a09072cfd84c78e6e15ec52039f5))
* allow to set randomizationFactor to 0 ([#1447](https://github.com/socketio/socket.io-client/issues/1447)) ([dfb46b5](https://github.com/socketio/socket.io-client/commit/dfb46b55a55d9c5b0397f4bc0fab9cec99ff430e))


### Features

* add an option to use native timer functions ([#1479](https://github.com/socketio/socket.io-client/issues/1479)) ([4e1b656](https://github.com/socketio/socket.io-client/commit/4e1b65699d9967a7bb409bdc89c894c62562771b))


## [4.1.3](https://github.com/socketio/socket.io-client/compare/4.1.2...4.1.3) (2021-07-10)


## [4.1.2](https://github.com/socketio/socket.io-client/compare/4.1.1...4.1.2) (2021-05-17)


### Bug Fixes

* **typings:** add missing closeOnBeforeunload option ([#1469](https://github.com/socketio/socket.io-client/issues/1469)) ([35d27df](https://github.com/socketio/socket.io-client/commit/35d27df2ae48046bfe3ae2e11f82004200095aae))
* **typings:** add missing requestTimeout option ([#1467](https://github.com/socketio/socket.io-client/issues/1467)) ([c8dfbb1](https://github.com/socketio/socket.io-client/commit/c8dfbb1c1d10aff16bc19cc1f1bab6b3a9240d81))


## [4.1.1](https://github.com/socketio/socket.io-client/compare/4.1.0...4.1.1) (2021-05-11)

There were some minor bug fixes on the server side, which mandate a client bump.


# [4.1.0](https://github.com/socketio/socket.io-client/compare/4.0.2...4.1.0) (2021-05-11)

### Features

* add the "closeOnBeforeunload" option ([dcb85e9](https://github.com/socketio/engine.io-client/commit/dcb85e902d129b2d1a94943b4f6d471532f70dc9), from `engine.io-client`)


## [4.0.2](https://github.com/socketio/socket.io-client/compare/4.0.1...4.0.2) (2021-05-06)


### Bug Fixes

* **typings:** add fallback to untyped event listener ([5394669](https://github.com/socketio/socket.io-client/commit/53946694882114957ef2187c532eb798fa811b60))
* ensure buffered events are sent in order ([34f822f](https://github.com/socketio/socket.io-client/commit/34f822f783c6985039c0733a96d1fab8f01b1edf))
* ensure connections are properly multiplexed ([dd2a8fc](https://github.com/socketio/socket.io-client/commit/dd2a8fce000a9b5b5d741489fc44eafd4ff6c75b))
* properly export the Socket class ([e20d487](https://github.com/socketio/socket.io-client/commit/e20d487ac080910c90e7b766f8509f5e40c9ecfe))


## [4.0.1](https://github.com/socketio/socket.io-client/compare/4.0.0...4.0.1) (2021-03-31)


### Bug Fixes

* **typings:** make `auth` property public ([#1455](https://github.com/socketio/socket.io-client/issues/1455)) ([c150223](https://github.com/socketio/socket.io-client/commit/c15022347c662dc31ee0a3d89cde23641f029783))
* **typings:** update definition to match wrapper.mjs ([#1456](https://github.com/socketio/socket.io-client/issues/1456)) ([48f573f](https://github.com/socketio/socket.io-client/commit/48f573f6f6c4d542e6a098e7f4ae472b888b5664))



## [3.1.3](https://github.com/socketio/socket.io-client/compare/3.1.2...3.1.3) (2021-03-12)


### Bug Fixes

* **bundle:** restore support for JS modules ([afa7953](https://github.com/socketio/socket.io-client/commit/afa79532f8a422cc9246175abdbe30299a0b0281))



# [4.0.0](https://github.com/socketio/socket.io-client/compare/3.1.2...4.0.0) (2021-03-10)

The major bump is due to some breaking changes on the server side.

### Bug Fixes

* **bundle:** restore support for JS modules ([43613d1](https://github.com/socketio/socket.io-client/commit/43613d1b2c3c04e89d572750656012f54d44467c))


### Features

* add autoUnref option ([6abfa1f](https://github.com/socketio/socket.io-client/commit/6abfa1fa4c7fea0d69c69b254d2e1ca18f19c4bc))
* add support for typed events ([5902365](https://github.com/socketio/socket.io-client/commit/59023657a02cf78f90522e0d7797749707ed5ed2))


## [3.1.2](https://github.com/socketio/socket.io-client/compare/3.1.1...3.1.2) (2021-02-26)


### Bug Fixes

* restore support for web workers ([13b32b3](https://github.com/socketio/socket.io-client/commit/13b32b39a4c1cf4829144fb0a95c4d0506000fb3))
* silently close the transport in the beforeunload hook ([ed48b5d](https://github.com/socketio/engine.io-client/commit/ed48b5dc3407e5ded45072606b3bb0eafa49c01f), from `engine.io-client`)


## [3.1.1](https://github.com/socketio/socket.io-client/compare/3.1.0...3.1.1) (2021-02-03)


### Bug Fixes

* include the path in the manager ID ([7a0c2b5](https://github.com/socketio/socket.io-client/commit/7a0c2b504f5f3bac64d423684fb1bb44229c7a70))
* remove polyfill for process in the bundle ([61afc5d](https://github.com/socketio/socket.io-client/commit/61afc5d8cb9f10985930b2f01758089c49f84686))
* **typings:** add return types and general-case overload signatures ([#1440](https://github.com/socketio/socket.io-client/issues/1440)) ([47f917a](https://github.com/socketio/socket.io-client/commit/47f917afdd1821079723542f081c726596f2aaf3))
* **typings:** fix the type of the "query" option ([#1439](https://github.com/socketio/socket.io-client/issues/1439)) ([f02ab3b](https://github.com/socketio/socket.io-client/commit/f02ab3bc9626133dd35aad0916325f0c7fc4da5d))


# [3.1.0](https://github.com/socketio/socket.io-client/compare/3.0.5...3.1.0) (2021-01-15)


### Bug Fixes

* **typings:** make Manager#opts public ([#1437](https://github.com/socketio/socket.io-client/issues/1437)) ([fe97243](https://github.com/socketio/socket.io-client/commit/fe97243fab02cd80fc1116e8f4aeca02951dac75))
* allow integers as event names ([1c220dd](https://github.com/socketio/socket.io-parser/commit/1c220ddbf45ea4b44bc8dbf6f9ae245f672ba1b9))


## [3.0.5](https://github.com/socketio/socket.io-client/compare/3.0.4...3.0.5) (2021-01-05)


### Bug Fixes

* emit a connect_error event upon connection failure ([53c7374](https://github.com/socketio/socket.io-client/commit/53c73749a829b2c98d9a5e45c48f0ae5a22c056c))
* **typings:** make sendBuffer and receiveBuffer public ([b83f89c](https://github.com/socketio/socket.io-client/commit/b83f89c901e82e06f66cbda4124cf739d2bb01c3))



# [2.4.0](https://github.com/socketio/socket.io-client/compare/2.3.1...2.4.0) (2021-01-04)

The minor bump is matching the bump of the server, but there is no new feature in this release.



## [3.0.4](https://github.com/socketio/socket.io-client/compare/3.0.3...3.0.4) (2020-12-07)


### Bug Fixes

* emit an error when reaching a v2.x server ([ec1f8c3](https://github.com/socketio/socket.io-client/commit/ec1f8c3474b54600420487a0554cb195cc78f2bc)), closes [/github.com/socketio/engine.io-protocol#difference-between-v3-and-v4](https://github.com//github.com/socketio/engine.io-protocol/issues/difference-between-v3-and-v4) [/github.com/socketio/socket.io-protocol#difference-between-v5-and-v4](https://github.com//github.com/socketio/socket.io-protocol/issues/difference-between-v5-and-v4)
* keep track of active sockets ([f8f60fc](https://github.com/socketio/socket.io-client/commit/f8f60fc860f51aa6465fc32dd9275a8e1d22f05d))
* **typings:** export extraHeaders option ([#1410](https://github.com/socketio/socket.io-client/issues/1410)) ([b3de861](https://github.com/socketio/socket.io-client/commit/b3de861a928c0eb5f0b2f37956c671e72432715d))


## [3.0.3](https://github.com/socketio/socket.io-client/compare/3.0.2...3.0.3) (2020-11-19)


### Bug Fixes

* properly export io in ES modules wrapper ([bec1524](https://github.com/socketio/socket.io-client/commit/bec15240ea67e9d296ac94093974d7d831239e8d))


## [3.0.2](https://github.com/socketio/socket.io-client/compare/3.0.1...3.0.2) (2020-11-17)


### Bug Fixes

* **typings:** export withCredentials option ([7193078](https://github.com/socketio/socket.io-client/commit/719307801a2170f02d3a16ab52752ac219ca4b6e))
* **typings:** export ManagerOptions ([#1398](https://github.com/socketio/socket.io-client/issues/1398)) ([96cd2c9](https://github.com/socketio/socket.io-client/commit/96cd2c9ae4c48f9d2e6638ab26074277a3a6cf6b))
* add io as named exports ([7b3ec9f](https://github.com/socketio/socket.io-client/commit/7b3ec9fad9df9d2f030f644a26fcd642bf2a91ab))


## [3.0.1](https://github.com/socketio/socket.io-client/compare/3.0.0...3.0.1) (2020-11-09)


### Bug Fixes

* **typings:** export Socket and SocketOptions types ([#1394](https://github.com/socketio/socket.io-client/issues/1394)) ([19ab1e9](https://github.com/socketio/socket.io-client/commit/19ab1e9e4e1373d4ef4dad5381c8ae24167f5d89))


# [3.0.0](https://github.com/socketio/socket.io-client/compare/2.3.1...3.0.0) (2020-11-05)

### Code Refactoring

* rename ERROR to CONNECT_ERROR ([13e1db7](https://github.com/socketio/socket.io-client/commit/13e1db7c94291c583d843beaa9e06ee041ae4f26))

### Features

* emit an Error object upon middleware error ([0939395](https://github.com/socketio/socket.io-client/commit/09393952e3397a0c71f239ea983f8ec1623b7c21))
* add bundle with msgpack parser ([71d6048](https://github.com/socketio/socket.io-client/commit/71d60480af9ea06d22792540dafb18a76e9362e7))
* add support for catch-all listeners ([55f464f](https://github.com/socketio/socket.io-client/commit/55f464f59ed523fa1c1948ec10752bfdf808262d))
* add volatile events ([7ddad2c](https://github.com/socketio/socket.io-client/commit/7ddad2c09dea0391b20378ef03b40040f0230d3e))
* move binary detection back to the parser ([1789094](https://github.com/socketio/socket.io-client/commit/178909471a3dd232e71cba83b729b4cc66f1412f))
* add ES6 module export ([cbabb03](https://github.com/socketio/socket.io-client/commit/cbabb0308ef4f7d302654755e08fe2103b9f22c8))
* do not reuse the Engine.IO id ([bbe94ad](https://github.com/socketio/socket.io-client/commit/bbe94adb822a306c6272e977d394e3e203cae25d))
* remove the implicit connection to the default namespace ([249e0be](https://github.com/socketio/socket.io-client/commit/249e0bef9071e7afd785485961c4eef0094254e8))
* split the events of the Manager and Socket ([132f8ec](https://github.com/socketio/socket.io-client/commit/132f8ec918a596eec872aee0c61d4ce63714c400))
* throw upon reserved event names ([6494f61](https://github.com/socketio/socket.io-client/commit/6494f61be0d38d267d77c30ea4f43941f97b1bc0))

### BREAKING CHANGES

* the Socket instance will now emit a "connect_error" event instead of "error" (which is not a reserved event anymore)

```js
// before
socket.on("error", () => {});

// after
socket.on("connect_error", () => {});
```

* the Socket#binary() method is removed, as this use case is now covered by the ability to provide your own parser.

* the Socket instance will no longer forward the events of its Manager

Those events can still be accessed on the Manager instance though:

```js
socket.io.on("reconnect", () => {
  // ...
});
```

# [3.0.0-rc4](https://github.com/socketio/socket.io-client/compare/3.0.0-rc3...3.0.0-rc4) (2020-10-30)


### Features

* emit an Error object upon middleware error ([0939395](https://github.com/socketio/socket.io-client/commit/09393952e3397a0c71f239ea983f8ec1623b7c21))



# [3.0.0-rc3](https://github.com/socketio/socket.io-client/compare/3.0.0-rc2...3.0.0-rc3) (2020-10-26)


### Code Refactoring

* rename ERROR to CONNECT_ERROR ([13e1db7](https://github.com/socketio/socket.io-client/commit/13e1db7c94291c583d843beaa9e06ee041ae4f26))


### Features

* add bundle with msgpack parser ([71d6048](https://github.com/socketio/socket.io-client/commit/71d60480af9ea06d22792540dafb18a76e9362e7))
* add support for catch-all listeners ([55f464f](https://github.com/socketio/socket.io-client/commit/55f464f59ed523fa1c1948ec10752bfdf808262d))
* add volatile events ([7ddad2c](https://github.com/socketio/socket.io-client/commit/7ddad2c09dea0391b20378ef03b40040f0230d3e))


### BREAKING CHANGES

* the Socket instance will now emit a "connect_error" event instead of "error" (which is not a reserved event anymore)

```js
// before
socket.on("error", () => {});

// after
socket.on("connect_error", () => {});
```



# [3.0.0-rc2](https://github.com/socketio/socket.io-client/compare/3.0.0-rc1...3.0.0-rc2) (2020-10-15)


### Features

* move binary detection back to the parser ([1789094](https://github.com/socketio/socket.io-client/commit/178909471a3dd232e71cba83b729b4cc66f1412f))


### BREAKING CHANGES

* the Socket#binary() method is removed, as this use case is now covered by the ability to provide your own parser.



# [3.0.0-rc1](https://github.com/socketio/socket.io-client/compare/2.3.1...3.0.0-rc1) (2020-10-13)


### Features

* add ES6 module export ([cbabb03](https://github.com/socketio/socket.io-client/commit/cbabb0308ef4f7d302654755e08fe2103b9f22c8))
* do not reuse the Engine.IO id ([bbe94ad](https://github.com/socketio/socket.io-client/commit/bbe94adb822a306c6272e977d394e3e203cae25d))
* remove the implicit connection to the default namespace ([249e0be](https://github.com/socketio/socket.io-client/commit/249e0bef9071e7afd785485961c4eef0094254e8))
* split the events of the Manager and Socket ([132f8ec](https://github.com/socketio/socket.io-client/commit/132f8ec918a596eec872aee0c61d4ce63714c400))
* throw upon reserved event names ([6494f61](https://github.com/socketio/socket.io-client/commit/6494f61be0d38d267d77c30ea4f43941f97b1bc0))


### BREAKING CHANGES

* the Socket instance will no longer forward the events of its Manager

Those events can still be accessed on the Manager instance though:

```js
socket.io.on("reconnect", () => {
  // ...
});
```


## [2.3.1](https://github.com/socketio/socket.io-client/compare/2.3.0...2.3.1) (2020-09-30)

The `debug` dependency has been reverted to `~3.1.0`, as the newer versions contains ES6 syntax which breaks in IE
browsers.

Please note that this only applied to users that bundle the Socket.IO client in their application, with webpack for
example, as the "official" bundles (in the dist/ folder) were already transpiled with babel.

For webpack users, you can also take a look at the [webpack-remove-debug](https://github.com/johngodley/webpack-remove-debug)
plugin.

### Bug Fixes

* fix reconnection after opening socket asynchronously ([#1253](https://github.com/socketio/socket.io-client/issues/1253)) ([050108b](https://github.com/socketio/socket.io-client/commit/050108b2281effda086b197cf174ee2e8e1aad79))



# [2.3.0](https://github.com/socketio/socket.io-client/compare/2.2.0...2.3.0) (2019-09-20)

The minor bump is matching the bump of the server, but there is no new feature in this release.



# [2.2.0](https://github.com/socketio/socket.io-client/compare/2.1.1...2.2.0) (2018-11-29)

### Bug fixes

- remove any reference to the `global` variable (related: https://github.com/socketio/socket.io-client/issues/1166)



## [2.1.1](https://github.com/socketio/socket.io-client/compare/2.1.0...2.1.1) (2018-05-17)

### Bug fixes

- fire an error event on middleware failure for non-root namespace ([#1202](https://github.com/socketio/socket.io-client/issues/1202)) ([0fe9439](https://github.com/socketio/socket.io-client/commit/0fe9439ff6d97fb6e7fa7bd145ee9367de055b29))



# [2.1.0](https://github.com/socketio/socket.io-client/compare/2.0.4...2.1.0) (2018-03-29)

### Features

- add a 'binary' flag ([#1194](https://github.com/socketio/socket.io-client/pull/1194)) ([74893d5](https://github.com/socketio/socket.io-client/commit/74893d53ca22335cbdbdd1468a5f9a810143a231))

```js
// by default, the object is recursively scanned to check whether it contains some binary data
// in the following example, the check is skipped in order to improve performance
socket.binary(false).emit('plain-object', object);
```
