memoryTransport

Routes realtime events by topic inside one process, with no server and no library. For tests and demos: it reaches one page, not another browser.

memoryTransport is the transport the demos and the tests run on. It holds the subscribers of each topic in a Map and hands each publish straight to them.

Signature

function memoryTransport(options?: MemoryTransportOptions): MemoryTransport
 
interface MemoryTransportOptions {
  /** Waits this long between recording a publish and delivering it. */
  delayMs?: number;
  /** Called for every transport error, like a listener from `onError()`. */
  onError?: (error: RealtimeTransportError) => void;
}

Returns

A MemoryTransport: every member of RealtimeTransport (subscribe, publish, onReconnect, onStatusChange, getStatus and onError) plus three members tests and demos drive it with.

Member	Does
`publishedEvents`	Every event published so far, in order, whether or not anyone listened
`simulateReconnect()`	Calls every `onReconnect` listener, as a transport does after a drop
`setStatus(status)`	Sets what `getStatus` reports and calls every `onStatusChange` listener

It starts as "connected", since there is no connection to open.

publish records the event first, then waits delayMs, then dispatches. An unsubscribe during that delay is honoured, so the callback is not called.
A subscriber that throws is reported as handler_threw, and the other subscribers still run.
Nothing leaves the process. Two components in one tab share events; a second tab of the browser does not, and neither does another device. For the tabs of one browser, use broadcastChannelTransport.

Example

import { memoryTransport } from "@chelone/core";
 
export const transport = memoryTransport({
  delayMs: 50,
  onError: (error) => console.error(error.kind, error.cause),
});
 
const stop = transport.subscribe("resource/posts", (event) =>
  console.log(event.type),
);
 
await transport.publish("resource/posts", {
  type: "updated",
  payload: { ids: [1] },
});
 
transport.publishedEvents.length; // 1
transport.simulateReconnect();
stop();

See the realtime guide for the transport contract, the other transports and the status each one reports.