Port+ – Advanced Web Messaging Primitives

Port+ is an upgrade to the web's port-based messaging APIs — MessagePort, MessageChannel, BroadcastChannel – and an onboarding of the WebSocket API into the same port-based messaging model.

This README takes you from installation to the design concepts and, ultimately, to the added capabilities implied by Port+.

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Install

npm i @webqit/port-plus

import { MessageChannelPlus, BroadcastChannelPlus, WebSocketPort, ... } from '@webqit/port-plus';

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Design Concepts

Port+ is an API mirror of the Web Messaging APIs built for advanced use cases. An instance of BroadcastChannelPlus, for example, gives you the same standard BroadcastChannel instance, but better.

The following is the mental model of the existing Web Messaging APIs. The Port+ equivalent comes next.

(a) The Web's Messaging APIs at a Glance

1. MessageChannel

MessageChannel (ch)
  ├─ ch.port1 ──► MessageEvent (e) ──► e.ports
  └─ ch.port2 ──► MessageEvent (e) ──► e.ports

In this system:

• ch.port1 and ch.port2 are each a message port (MessagePort)
• messages (e) arrive as message events (MessageEvent)
• e.ports are each a message port (MessagePort)

2. BroadcastChannel

BroadcastChannel (br) ──► MessageEvent (e)

In this system:

• the BroadcastChannel interface is the message port – the equivalent of MessagePort
• messages (e) arrive as message events (MessageEvent)
• no reply ports – e.ports; not implemented in BroadcastChannel

3. WebSocket

WebSocket ──► MessageEvent (e)

In this system:

• the WebSocket interface is partly a message port (having addEventListener()) and partly not (no postMessage())
• messages (e) arrive as message events (MessageEvent)
• no reply ports – e.ports; not implemented in WebSocket
• no API parity with MessagePort / BroadcastChannel in all

(b) The Port+ Equivalent

1. MessageChannelPlus

MessageChannelPlus (ch)
  ├─ ch.port1+ ──► MessageEventPlus (e) ──► e.ports+
  └─ ch.port2+ ──► MessageEventPlus (e) ──► e.ports+

2. BroadcastChannelPlus

BroadcastChannelPlus (br) ──► MessageEventPlus (e) ──► e.ports+

3. WebSocketPort (WebSocket)

WebSocketPort ──► MessageEventPlus (e) ──► e.ports+

(c) Result

Port+ unifies the messaging model across all three and extends the port interfaces and MessageEvent interface for advanced use cases.

General mental model:

port+ ──► MessageEventPlus ──► e.ports+

Meaning: Port+ interfaces emit MessageEventPlus, which recursively exposes e.ports as Port+ interface.

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The Port+ API Overview

1. Port-Level API

API / Feature	Port+	Msg. Ports	WS
postMessage()	✓ (advanced)	✓ (basic)	✗ (send())
addEventListener() / onmessage	✓	✓	✓
close()	✓	✓	✓
readyState	✓	✗	✓
readyStateChange()	✓	✗	✗
postRequest()	✓	✗	✗
handleRequests()	✓	✗	✗
relay()	✓	✗	✗
channel()	✓	✗	✗
projectMutations()	✓	✗	✗
Live Objects**	✓	✗	✗

In this table:

• Port+ → MessagePortPlus, BroadcastChannelPlus, WebSocketPort
• Msg. Ports → MessagePort, BroadcastChannel
• WS → WebSocket
• ** → All-new concept

2. Message-Level API

API / Feature	Port+	Msg. Event	WS
data	✓ (Live Objects support)	✓ (no Live Objects)	✓ (typically string)
type	✓	✓	✓
ports	✓ (Port+)	✓**	✗**
preventDefault()	✓	✓	✗**
defaultPrevented	✓	✓	✗**
stopPropagation()	✓	✓	✗**
stopImmediatePropagation()	✓	✓	✗**
respondWith()	✓	✗	✗
eventID	✓	✗	✗
live	✓	✗	✗
relayedFrom	✓	✗	✗

In this table:

• Port+ → MessageEventPlus
• Msg. Event → MessageEvent
• WS → WebSocket's MessageEvent
• ** → May be present, but may not be implemented

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Entry Points

The APIs below are the entry points to a Port+-based messaging system.

const ch = new MessageChannelPlus();
const br = new BroadcastChannelPlus('channel-name');
const soc = new WebSocketPort(url); // or new WebSocketPort(ws)

Above, WebSocketPort also takes a WebSocket instance – letting you create a port from an existing WebSocket connection:

const ws = new WebSocket(url);
const port = new WebSocketPort(ws);

On a WebSocket server, for example, you can do:

const wss = new WebSocketServer({ server });
wss.on('connection', (ws) => {
    // The basic way
    ws.send('something');

    // The unified way
    const port = new WebSocketPort(ws);
    port.postMessage('something');
});

Whatever the Port+ instance, it always has the same API and set of capabilities. For example, with WebSocketPort you get an event.ports implementation over web sockets.

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Capabilities

TODO Live Objects Lifecycle APIs Request / Response Messaging Forwarding and Topologies

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License

MIT.