altamoon-robust-websocket

robust-websocket

A robust, reconnecting WebSocket client for the browser

robust-websocket is a wrapper around the standard WebSocket class that implements the same interface, but can reconnect when disconnected or the user's computer comes back online.

It is error-code aware and will not reconnect on 1008 (HTTP 400 equivalent) and 1011 (HTTP 500 equivalent) by default. This behavior is fully configurable via the shouldConnect (see Usage).

Compared to reconnecting-websocket

• Tests! You know it works like stated and regressions will be caught.
• Is aware of online and offline, and won't burn up the users battery and CPU reconnected when offline, and will reconnect when it is online again.
• Natively aware of error codes
• Any kind of reconnect strategy is possible via functional composition

Usage

CodePen Example

Use it as you would a normal websocket:

var ws = new RobustWebSocket('ws://echo.websocket.org/')

ws.addEventListener('open', function(event) {
  ws.send('Hello!')
})

ws.addEventListener('message', function(event) {
  console.log('we got: ' + event.data)
})

But with an optional set of options you can specify as a 3rd parameter

var ws = new RobustWebSocket('ws://echo.websocket.org/', {
   // The number of milliseconds to wait before a connection is considered to have timed out. Defaults to 4 seconds.
   timeout: 4000,
  // A function that given a CloseEvent or an online event (https://developer.mozilla.org/en-US/docs/Online_and_offline_events) and the `RobustWebSocket`,
  // will return the number of milliseconds to wait to reconnect, or a non-Number to not reconnect.
  // see below for more examples; below is the default functionality.
  shouldReconnect: function(event, ws) {
    if (event.code === 1008 || event.code === 1011) return
    return [0, 3000, 10000][ws.attempts]
  },
  // A boolean indicating whether or not to open the connection automatically. Defaults to true, matching native [WebSocket] behavior.
  // You can open the websocket by calling `open()` when you are ready. You can close and re-open the RobustWebSocket instance as much as you wish.
  automaticOpen: true,
  // A boolean indicating whether to disable subscribing to the connectivity events provided by the browser.
  // By default RobustWebSocket instances use connectivity events to avoid triggering reconnection when the browser is offline. This flag is provided in the unlikely event of cases where this may not be desired.
  ignoreConnectivityEvents: false
})

The URL parameter can either be a string, or a function which returns a string. This can be useful if you need the WebSocket to reconnect to a different URL than it connected to initially:

var ws = new RobustWebSocket((ws) => {
  return ws.reconnects > 0 ? `ws://echo.websocket.org/?reconnect=${ws.reconnects}` : `ws://echo.websocket.org/`
});

shouldReconnect Examples

Reconnect with an exponetial backoff on all errors

function shouldReconnect(event, ws) {
  return Math.pow(1.5, ws.attempts) * 500
}

Reconnect immediately but only 20 times per RobustWebSocket instance

function shouldReconnect(event, ws) {
  return ws.reconnects <= 20 && 0
}

Reconnect only on some whitelisted codes, and only 3 attempts, except on online events, then connect immediately

function shouldReconnect(event, ws) {
  if (event.type === 'online') return 0
  return [1006,1011,1012].indexOf(event.code) && [1000,5000,10000][ws.attempts]
}

See documentation for CloseEvent and online event, the two types of events that shouldReconnect will receive.

Typically, websockets closed with code 1000 indicate that the socket closed normally. In these cases, robust-websocket won't call shouldReconnect (and will not attempt to reconnect), unless you set shouldReconnect.handle1000 to true.

Polyfills needed

You may need these polyfills to support older browsers

• Object.assign - npm package or 24-line MDN snippet
• CustomEvent - npm package or 15-line MDN snippet