learn-reconnecting-websocket

ReconnectingWebSocket

A small JavaScript library that decorates the WebSocket API to provide a WebSocket connection that will automatically reconnect if the connection is dropped.

It is API compatible, so when you have:

var ws = new WebSocket('ws://....');

you can replace with:

var ws = new ReconnectingWebSocket('ws://....');

Minified library with gzip compression is less than 600 bytes.

How reconnections occur

With the standard WebSocket API, the events you receive from the WebSocket instance are typically:

onopen
onmessage
onmessage
onmessage
onclose // At this point the WebSocket instance is dead.

With a ReconnectingWebSocket, after an onclose event is called it will automatically attempt to reconnect. In addition, a connection is attempted repeatedly (with a small pause) until it succeeds. So the events you receive may look something more like:

onopen
onmessage
onmessage
onmessage
onclose
// ReconnectingWebSocket attempts to reconnect
onopen
onmessage
onmessage
onmessage
onclose
// ReconnectingWebSocket attempts to reconnect
onopen
onmessage
onmessage
onmessage
onclose

This is all handled automatically for you by the library.

Parameters

var socket = new ReconnectingWebSocket(url, protocols, options);

url

• The URL you are connecting to.
• https://html.spec.whatwg.org/multipage/comms.html#network

protocols

• Optional string or array of protocols per the WebSocket spec.
• https://tools.ietf.org/html/rfc6455

options

• Options (see below)

Options

Options can either be passed as the 3rd parameter upon instantiation or set directly on the object after instantiation:

var socket = new ReconnectingWebSocket(url, null, {debug: true, reconnectInterval: 3000});

or

var socket = new ReconnectingWebSocket(url);
socket.debug = true;
socket.timeoutInterval = 5400;

debug

• Whether this instance should log debug messages or not. Debug messages are printed to console.debug().
• Accepts true or false
• Default value: false

automaticOpen

• Whether or not the websocket should attempt to connect immediately upon instantiation. The socket can be manually opened or closed at any time using ws.open() and ws.close().
• Accepts true or false
• Default value: true

reconnectInterval

• The number of milliseconds to delay before attempting to reconnect.
• Accepts integer
• Default: 1000

maxReconnectInterval

• The maximum number of milliseconds to delay a reconnection attempt.
• Accepts integer
• Default: 30000

####reconnectDecay

• The rate of increase of the reconnect delay. Allows reconnect attempts to back off when problems persist.
• Accepts integer or float
• Default: 1.5

timeoutInterval

• The maximum time in milliseconds to wait for a connection to succeed before closing and retrying.
• Accepts integer
• Default: 2000

maxReconnectAttempts

• The maximum number of reconnection attempts that will be made before giving up. If null, reconnection attempts will be continue to be made forever.
• Accepts integer or null.
• Default: null

binaryType

• The binary type is required by some applications.
• Accepts strings 'blob' or 'arraybuffer'.
• Default: 'blob'

---

Methods

ws.open()

• Open the Reconnecting Websocket

ws.close(code, reason)

• Closes the WebSocket connection or connection attempt, if any. If the connection is already CLOSED, this method does nothing.
• code is optional the closing code (default value 1000). https://tools.ietf.org/html/rfc6455#section-7.4.1
• reason is the optional reason that the socket is being closed. https://tools.ietf.org/html/rfc6455#section-7.1.6

ws.refresh()

• Refresh the connection if still open (close and then re-open it).

ws.send(data)

• Transmits data to the server over the WebSocket connection.
• Accepts @param data a text string, ArrayBuffer or Blob

Like this? Check out websocketd for the simplest way to create WebSocket backends from any programming language.

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