zen-observable

What is zen-observable?

The zen-observable npm package provides an implementation of the Observable pattern, which is used for managing asynchronous data streams. It allows you to create, transform, and subscribe to data streams in a declarative manner.

What are zen-observable's main functionalities?

Creating an Observable

This feature allows you to create a new Observable instance. The observer object is used to emit values and signal completion. The subscriber receives these values and handles them accordingly.

const { Observable } = require('zen-observable');

const observable = new Observable(observer => {
  observer.next('Hello');
  observer.next('World');
  observer.complete();
});

observable.subscribe({
  next(value) { console.log(value); },
  complete() { console.log('Done'); }
});

Transforming Observables

This feature allows you to transform the data emitted by an Observable using operators like map. In this example, each value emitted by the original Observable is multiplied by 2.

const { Observable } = require('zen-observable');

const observable = new Observable(observer => {
  observer.next(1);
  observer.next(2);
  observer.next(3);
  observer.complete();
});

const transformed = observable.map(x => x * 2);

transformed.subscribe({
  next(value) { console.log(value); },
  complete() { console.log('Done'); }
});

Combining Observables

This feature allows you to combine multiple Observables into a single Observable. In this example, two Observables are combined and their values are emitted in sequence.

const { Observable } = require('zen-observable');

const observable1 = new Observable(observer => {
  observer.next('A');
  observer.complete();
});

const observable2 = new Observable(observer => {
  observer.next('B');
  observer.complete();
});

const combined = Observable.from([observable1, observable2]).flatMap(x => x);

combined.subscribe({
  next(value) { console.log(value); },
  complete() { console.log('Done'); }
});

Other packages similar to zen-observable

rxjs

RxJS is a library for reactive programming using Observables, to make it easier to compose asynchronous or callback-based code. It is more feature-rich compared to zen-observable and includes a wide range of operators for transforming, combining, and querying Observables.

baconjs

Bacon.js is a functional reactive programming library for JavaScript. It provides a comprehensive set of tools for working with event streams and properties. Compared to zen-observable, Bacon.js offers more advanced features for handling complex data flows.

most

Most.js is a high-performance reactive programming library that focuses on speed and efficiency. It provides a minimalistic API for working with streams. While zen-observable is simpler and easier to use, most.js is optimized for performance and can handle large-scale data streams more efficiently.

README

zen-observable

An implementation of ES Observables.

Requires ES6 Promises or a Promise polyfill.

Install

npm install zen-observable

Download

• zen-observable.js

Usage

Node:

var Observable = require("zen-observable");
Observable.of(1, 2, 3).subscribe(x => console.log(x));

Browser:

<script src="zen-observable.js"></script>
<script>
    Observable.of(1, 2, 3).subscribe(x => console.log(x));
</script>

ES Modules:

import Observable from "zen-observable";
Observable.of(1, 2, 3).subscribe(x => console.log(x));

API

new Observable ( subscribe )

let observable = new Observable(observer => {
    // Emit a single value after 1 second
    let timer = setTimeout(_=> {
        observer.next("hello");
        observer.complete();
    }, 1000);

    // On unsubscription, cancel the timer
    return _=> clearTimeout(timer);
});

Creates a new Observable object using the specified subscriber function. The subscriber function is called whenever the subscribe method of the observable object is invoked. The subscriber function is passed an observer object which has the following methods:

• next(value) Sends the next value in the sequence.
• error(exception) Terminates the sequence with an exception.
• complete() Terminates the sequence successfully.

The subscriber function can optionally return either a cleanup function or a subscription object. If it returns a cleanup function, that function will be called when the subscription has closed. If it returns a subscription object, then the subscription's unsubscribe method will be invoked when the subscription has closed.

Observable.of ( ...items )

// Logs 1, 2, 3
Observable.of(1, 2, 3).subscribe(x => {
    console.log(x);
});

Returns an observable which will emit each supplied argument.

Observable.from ( value )

let list = [1, 2, 3];

// Iterate over an object
Observable.from(list).subscribe(x => {
    console.log(x);
});

// Convert something "observable" to an Observable instance
Observable.from(otherObservable).subscribe(x => {
    console.log(x);
});

Converts value to an Observable.

• If value is an implementation of ES Observables, then it is converted to an instance of Observable as defined by this library.
• Otherwise, it is converted to an Observable which synchronously iterates over value.

observable.subscribe ( observer )

let subscription = observable.subscribe({
    next(x) { console.log(x) },
    error(err) { console.log(`Finished with error: ${ err }`) },
    complete() { console.log("Finished") }
})

Subscribes to the observable. The observer argument must be an object. It may have any of the following methods:

• start(subscription) Receives the subscription object during initialization.
• next(value) Receives the next value of the sequence.
• error(exception) Receives the terminating error of the sequence.
• complete() Called when the stream has completed successfully.

The subscription object can be used to cancel the stream.

// Stop receiving data from the stream
subscription.unsubscribe();

Extended API

The following methods are not yet defined by the ES Observable specification.

observable.forEach ( callback )

observable.forEach(x => {
    console.log(`Received value: ${ x }`);
}).then(_=> {
    console.log("Finished successfully")
}).catch(err => {
    console.log(`Finished with error: ${ err }`);
})

Subscribes to the observable and returns a Promise for the completion value of the stream. The callback argument is called once for each value in the stream.

observable.filter ( callback )

Observable.of(1, 2, 3).filter(value => {
    return value > 2;
}).subscribe(value => {
    console.log(value);
});
// 3

Returns a new Observable that emits all values which pass the test implemented by the callback argument.

observable.map ( callback )

Returns a new Observable that emits the results of calling the callback argument for every value in the stream.

Observable.of(1, 2, 3).map(value => {
    return value * 2;
}).subscribe(value => {
    console.log(value);
});
// 2
// 4
// 6

observable.reduce ( callback [, initialValue] )

Observable.of(0, 1, 2, 3, 4).reduce((previousValue, currentValue) => {
    return previousValue + currentValue;
}).subscribe(result => {
    console.log(result);
});
// 10

Returns a new Observable that applies a function against an accumulator and each value of the stream to reduce it to a single value.