oja-pubsub


This module is a subset of eBay Oja framework.

The module defines generic actions that can be used to organize actions into publishers and subscribers that are completely disconnected from each others.

__Comparing to Oja v1.0 this one is pub/sub on steroids - it defines pub/sub pattern using dependency injection.__

Installation

``
$ npm install @ebay/oja-pubsub --save
`

Actions

* action(_'oja/subscribe'_, '_topic_', listener) - subscribe to the event.
* action('_oja/unsubscribe_', '_topic_', listener): Promise - unsubscribe from the event, returns true if subscriber was found and removed.
* action('_oja/dispatch_', '_topic_', ...args): Promise<[subscriberResponse]> - dispatch event/args to the subscribers.
* action('_oja/route_', '_topic_', ...args): Promise - dispatch event/args to only one subscriber in round robin mode.

Listener

`js
function (eventType, ...eventData) {}
`

Usage

* Subscribing to the event:

`js
const { createContext } = require('@ebay/oja-action');
const context = await createContext();
// subscribe
const listener = await context.action('oja/subscribe', 'topic', (eventType, eventData) => {
console.log(eventData);
});
`

* Dispatching an event:

`js
await context.action('oja/dispatch', 'topic', eventData);
`

* Routing an event to only one subscriber:

`js
const { createContext } = require('@ebay/oja-action');
const context = await createContext();
// subscribe
const listener1 = await context.action('oja/subscribe', 'topic', (eventType, eventData) => {
console.log('sub1', eventData); // >> one, three
return 'ok1';
});
const listener2 = await context.action('oja/subscribe', 'topic', (eventType, eventData) => {
console.log('sub2', eventData); // >> two, four
return 'ok2'
});
await context.action('oja/route', 'topic', 'one'); // >> ok1
await context.action('oja/route', 'topic', 'two'); // >> ok2
await context.action('oja/route', 'topic', 'three'); // >> ok1
await context.action('oja/route', 'topic', 'four'); // >> ok2
`

* Unsubscribing from the event:

`js
await context.action('oja/unsubscribe', 'topic', listener);
`

$3

`js
context => {
const listener = context.action(
'oja/subscribe', 'topic', (eventType, eventData) => {
console.log(eventData);
}
);
}
`

To trigger subscription, one needs to trigger the respective action.

Oja reset event

In some cases it may be required to reset any cache related to oja.

@ebay/oja-action makes an optional action call 'oja/extension/context/reset' that if extended can be used to reset respective caches. The only problem is it allows a single extenstion while we may need to reset more then one module.
That's where pub/sub pattern comes handy - the module extends reset action and dispatches the event that can be listened by many subscribers.

`js
// this examples requires these modules to be installed: oja-context, oja-action, oja-pubsub
// register reset listeners
await context.action('oja/subscribe', 'oja:reset:event', (eventType, eventData) => {
console.log('sub1:', eventType); // >>> sub1: oja:reset:event
console.log(eventData); // >>> undefined, nothing to dispatch yet
});

await context.action('oja/subscribe', 'oja:reset:event', (eventType, eventData) => {
console.log('sub2:', eventType); // >>> sub2: oja:reset:event
console.log(eventData); // >>> undefined, nothing to dispatch yet
});

// trigger reset somewhere in the code
await context.action('oja/reset');
``