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A simple pub/sub written in Typescript

Gist

import { Subscription } from 'suub';

const mySub = Subscription<number>();

const unsub = mySub.subscribe((num) => {
  console.log('num: ' + num);
});

mySub.emit(45); // num: 45

unsub();

Guide

Creating a Subscription

To create a Subscription you need to import the Subscription function and call it.

import { Subscription } from 'suub';

const subscription = Subscription();

If you use TypeScript, you need to pass a type parameter to the Subscription function to define the type of the value associated with the subscription. By default this type is void (no value).

import { Subscription } from 'suub';

const numSubscription = Subscription<number>();

Subscribe and Unsubscribe

You have two ways to subscribe / unsubscribe.

  • Using the reference of the callback function
const callback = () => {
  /*...*/
};

subscription.subscribe(callback);
// later
subscription.unsubscribe(callback);
  • Using a SubId (a string)
subscription.subscribe('mySubId', () => {
  /*...*/
});
// later
subscription.unsubscribe('mySubId');

In both case the subscribe return a function that will unsubscribe:

const unsub = subscription.subscribe(/*...*/);
// later
unsub();

Emitting value

To emit a value and trigger all subscribed callback you need to call the emit method.

subscription.emit(42);
// you can also emit with no value
subscription.emit();

OnUnsubscribe

The subscribe method accept a optional function after the callback, this function will be called when this callback you are subscribing is unsubscribed.

subscription.subscribe(
  () => {
    /* ... */
  },
  () => {
    console.log('Unsubscribed !');
  }
);

// or with a subId
subscription.subscribe(
  'mySub',
  () => {
    /* ... */
  },
  () => {
    console.log('Unsubscribed !');
  }
);

Unsubscribing all callback

You can call unsubscribeAll method on a subscription to remove all callback. This will also trigger the onUnsubscribe if any.

subscription.unsubscribeAll();

Subscription options

The Subscription function accept an option object as parameter (all properties are optional):

const sub = Subscription({
  onFirstSubscription: () => {},
  onLastUnsubscribe: () => {},
  maxSubscriptionCount: 10000,
  maxRecursiveCall: 1000,
});

onFirstSubscription

A function called when the number of subscribers goes from 0 to 1

onLastUnsubscribe

A function called when the number of subscribers goes from 1 to 0

maxSubscriptionCount

A number to limit the maximum number of simultaneous subscriptions (default is 10000). This limit exist to detect infinit subscription loop.

maxRecursiveCall

A number to limit the maximum recursive call of emit (defaumt is 1000). This limit exist to detect infinite loop where you emit in a callback.

Testing if a callback / subId is subscribed

The isSubscribed let you test whether or not a callback / subId is currently subscribed

subscription.isSubscribed(myCallback); // <- boolean
subscription.isSubscribed('my-sub-id'); // <- boolean

Reading the number of active Subscriptions

You can call the size method to get the number of subscriptions.

subscription.size();

Some precisions

Callback are called in the order they are subscribed.

If you re-subscribe the same callback it will not re-do a subscription but instead move the subscription to the end.

In other words, calling subscribe on an already subscribed callback or subId will not make the callback called twice. But it will move the callback at the end of the subscription list.

If you call unsubscribe in a callback it will have effect immediatly.

If the callback you unsubscribe is supposed to run after the current callback, it will not be called.

If you subscribe in a callback it will not be called immediatly.

But it will be in the next emit.

If you emit() in a callback it will defer the call to after the current emit is done.

If you subscribe / unsubscribe / emit in an onUnsubscribed it will behave the same as if it was in the callback itself

Examples

Take a look at the Examples folder.

API

export type Unsubscribe = () => void;
export type OnUnsubscribed = () => void;
export type SubscriptionCallback<T> = (value: T) => void;
export type VoidSubscriptionCallback = () => void;
export type UnsubscribeAllMethod = () => void;

export interface SubscribeMethod<T> {
  (callback: SubscriptionCallback<T>, onUnsubscribe?: OnUnsubscribed): Unsubscribe;
  (subId: string, callback: SubscriptionCallback<T>, onUnsubscribe?: OnUnsubscribed): Unsubscribe;
}

export interface VoidSubscribeMethod {
  (callback: VoidSubscriptionCallback, onUnsubscribe?: OnUnsubscribed): Unsubscribe;
  (subId: string, callback: VoidSubscriptionCallback, onUnsubscribe?: OnUnsubscribed): Unsubscribe;
}

export interface IsSubscribedMethod<T> {
  (subId: string): boolean;
  (callback: SubscriptionCallback<T>): boolean;
}

export interface UnsubscribeMethod<T> {
  (subId: string): void;
  (callback: SubscriptionCallback<T>): void;
}

export interface VoidIsSubscribedMethod {
  (subId: string): boolean;
  (callback: VoidSubscriptionCallback): boolean;
}

export interface VoidUnsubscribeMethod {
  (subId: string): void;
  (callback: VoidSubscriptionCallback): void;
}

export interface Subscription<T> {
  subscribe: SubscribeMethod<T>;
  unsubscribe: UnsubscribeMethod<T>;
  unsubscribeAll: UnsubscribeAllMethod;
  isSubscribed: IsSubscribedMethod<T>;
  size: () => number;
  emit: (newValue: T) => void;
}

export interface VoidSubscription {
  subscribe: VoidSubscribeMethod;
  unsubscribe: VoidUnsubscribeMethod;
  unsubscribeAll: UnsubscribeAllMethod;
  isSubscribed: VoidIsSubscribedMethod;
  size: () => number;
  emit: () => void;
}

export interface SubscriptionOptions {
  onFirstSubscription?: () => void;
  onLastUnsubscribe?: () => void;
  maxSubscriptionCount?: number;
  maxRecursiveCall?: number;
}

export function Subscription<T = void>(
  options: SubscriptionOptions = {}
): [T] extends [void] ? VoidSubscription : Subscription<T>;