reconnecting-websocket/README.md

# Reconnecting WebSocket

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WebSocket that will automatically reconnect if the connection is closed.

## Features

-   WebSocket API compatible (same interface, Level0 and Level2 event model)
-   Fully configurable
-   Multi-platform (Web, ServiceWorkers, Node.js, React Native)
-   Dependency free (does not depend on Window, DOM or any EventEmitter library)
-   Handle connection timeouts
-   Allows changing server URL between reconnections
-   Buffering. Will send accumulated messages on open
-   Multiple builds available (see dist folder)
-   Debug mode

## Install

```bash
npm install --save reconnecting-websocket
```

## Usage

### Compatible with WebSocket Browser API

So this documentation should be valid:
[MDN WebSocket API](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket).

Ping me if you find any problems. Or, even better, write a test for your case and make a pull
request :)

### Simple usage

```javascript
import ReconnectingWebSocket from 'reconnecting-websocket';

const rws = new ReconnectingWebSocket('ws://my.site.com');

rws.addEventListener('open', () => {
    rws.send('hello!');
});
```

### Update URL

The `url` parameter will be resolved before connecting, possible types:

-   `string`
-   `() => string`
-   `() => Promise<string>`

```javascript
import ReconnectingWebSocket from 'reconnecting-websocket';

const urls = ['ws://my.site.com', 'ws://your.site.com', 'ws://their.site.com'];
let urlIndex = 0;

// round robin url provider
const urlProvider = () => urls[urlIndex++ % urls.length];

const rws = new ReconnectingWebSocket(urlProvider);
```

```javascript
import ReconnectingWebSocket from 'reconnecting-websocket';

// async url provider
const urlProvider = async () => {
    const token = await getSessionToken();
    return `wss://my.site.com/${token}`;
};

const rws = new ReconnectingWebSocket(urlProvider);
```

### Options

#### Sample with custom options

```javascript
import ReconnectingWebSocket from 'reconnecting-websocket';
import WS from 'ws';

const options = {
    WebSocket: WS, // custom WebSocket constructor
    connectionTimeout: 1000,
    maxRetries: 10,
};
const rws = new ReconnectingWebSocket('ws://my.site.com', [], options);
```

#### Available options

```typescript
type Options = {
    WebSocket?: any; // WebSocket constructor, if none provided, defaults to global WebSocket
    maxReconnectionDelay?: number; // max delay in ms between reconnections
    minReconnectionDelay?: number; // min delay in ms between reconnections
    reconnectionDelayGrowFactor?: number; // how fast the reconnection delay grows
    minUptime?: number; // min time in ms to consider connection as stable
    connectionTimeout?: number; // retry connect if not connected after this time, in ms
    maxRetries?: number; // maximum number of retries
    maxEnqueuedMessages?: number; // maximum number of messages to buffer until reconnection
    startClosed?: boolean; // start websocket in CLOSED state, call `.reconnect()` to connect
    debug?: boolean; // enables debug output
};
```

#### Default values

```javascript
WebSocket: undefined,
maxReconnectionDelay: 10000,
minReconnectionDelay: 1000 + Math.random() * 4000,
reconnectionDelayGrowFactor: 1.3,
minUptime: 5000,
connectionTimeout: 4000,
maxRetries: Infinity,
maxEnqueuedMessages: Infinity,
startClosed: false,
debug: false,
```

## API

### Methods

```typescript
constructor(url: UrlProvider, protocols?: string | string[], options?: Options)

close(code?: number, reason?: string)
reconnect(code?: number, reason?: string)

send(data: string | ArrayBuffer | Blob | ArrayBufferView)

addEventListener(type: 'open' | 'close' | 'message' | 'error', listener: EventListener)
removeEventListener(type:  'open' | 'close' | 'message' | 'error', listener: EventListener)
```

### Attributes

[More info](https://developer.mozilla.org/en-US/docs/Web/API/WebSocket)

```typescript
binaryType: string;
bufferedAmount: number;
extensions: string;
onclose: EventListener;
onerror: EventListener;
onmessage: EventListener;
onopen: EventListener;
protocol: string;
readyState: number;
url: string;
retryCount: number;
```

### Constants

```text
CONNECTING 0 The connection is not yet open.
OPEN       1 The connection is open and ready to communicate.
CLOSING    2 The connection is in the process of closing.
CLOSED     3 The connection is closed or couldn't be opened.
```

## Contributing

[Read here](./CONTRIBUTING.md)

## License

MIT