shared-event-source

shared-event-source is a library that provides a shared EventSource connection across multiple browser tabs. It ensures that only one actual EventSource connection is open per URL, while other tabs receive events via a BroadcastChannel. This is particularly useful to get around the browser limit of maximum 6 non HTTP/2 SSE connections per domain.

Installation

Install the package via npm:

npm install shared-event-source

Usage

The SharedEventSource class mimics the standard EventSource API but uses a BroadcastChannel and the Web Locks API to coordinate state between tabs.

Example

import {SharedEventSource} from 'shared-event-source'

const eventSource = new SharedEventSource('https://example.com/events')

eventSource.onopen = () => {
  console.log('Connection opened')
}

eventSource.onmessage = (event) => {
  console.log('Message received:', event.data)
}

eventSource.onerror = () => {
  console.error('An error occurred')
}

// Close the connection when done
// eventSource.close()

Features

• Ensures only one EventSource connection per URL across all tabs.
• Automatically elects a new leader tab if the current leader closes.
• Broadcasts events to all tabs using the BroadcastChannel API.

API

SharedEventSource

Constructor

new SharedEventSource(url: string, eventSourceInitDict?: EventSourceInit)

• url: The URL of the server-sent events stream.
• eventSourceInitDict: Optional configuration, same as the standard EventSource.

Properties

• url: The URL of the EventSource.
• withCredentials: Whether credentials are included in the request.
• readyState: The current state of the connection (CONNECTING, OPEN, or CLOSED).
• onerror: Callback for error events.
• onmessage: Callback for message events.
• onopen: Callback for open events.

Methods

• close(): Closes the connection for this instance.

Static Constants

• CONNECTING: The connection is being established.
• OPEN: The connection is open and receiving events.
• CLOSED: The connection is closed.

Requirements

This library requires a browser environment with support for:

• BroadcastChannel
• Web Locks API

License

MIT