@hbieshaar/publisher

This module implements a publisher/subscription pattern with a twist.

The main addition to the pattern is that the subscribe() function has an additional parameter trigger. When trigger is set to true, a subscription will immediately trigger a 'resend' of the last publish data on the topic being subscrribed to.

create a Publisher

A Publisher can be created as a base-class, by a mixin to a class, or for a specific object.

base-class

The use as a base-class will not be common.

function DerivedClass() {
    Publisher.call(this);
}

Object.setPrototypeOf(DerivedClass.prototype, Publisher.prototype);

mixin on a class

The most common use will be as a mixin.

function MixedInClass() {
    Publisher.call(this);
}

Publisher.addTo(MixedInClass);

mixin on an object

Changing an object into a Publisher is not expected to be common.

const obj = { data: 3 };

Publisher.publishify(obj);

use a Publisher

Most of the functions in the publisher deal with the subscription to a topic. In the following examples, we assume there are 2 objects:

• pub the publisher object, and
• sub the subscriber object, and

a topic 'my data', whish returns a single value.

publish(topic, ...data)

pub.publish('my data', 4);

This call publishes the topic 'my data' to all subscriptions. It also stores that data in case a new subscription triggers a resend. So, this call might be usefull even if it is known that there can not be any subscribers yet.

subscribe(topic, callback, trigger=false)

Subscribe to a topic using

// create and save the callback
sub.cb = x => console.log('Just received', x);

pub.subscribe('my data', sub.cb, true);
// expect output
// Just received 4

The advantage of using trigger == true is an immediate initatization of the loosely coupled system.

unsubscribe(topic, callback)

To unsubscribe

pub.unsubscribe('my data', sub.cb);

once(topic, callback, trigger=false)

To subscribe to a topic for one publication

pub.once('my data', x => console.log('At last', x));
// expect nothing because `trigger == false`

pub.publish('my data', 5);
// expect output
// At last 5

pub.publish('my data', 6);
// expect nothing, there are no subscriptions anymore.

Further Documentation

The code in the file is easily readable, and well documented. The BitBucket repository has a JSDoc website.