rxjs

What is rxjs?

RxJS (Reactive Extensions for JavaScript) is a library for reactive programming using Observables, to make it easier to compose asynchronous or callback-based code. It provides an API for asynchronous programming with observable streams.

What are rxjs's main functionalities?

Creating Observables

This feature allows you to create an Observable stream of data. The code sample demonstrates how to create an Observable that emits several values over time.

const { Observable } = require('rxjs');

const observable = new Observable(subscriber => {
  subscriber.next(1);
  subscriber.next(2);
  subscriber.next(3);
  setTimeout(() => {
    subscriber.next(4);
    subscriber.complete();
  }, 1000);
});

Subscribing to Observables

This feature allows you to subscribe to an Observable and react to the data being emitted. The code sample shows how to subscribe to an Observable created from an array.

const { from } = require('rxjs');

const observable = from([10, 20, 30]);
const subscription = observable.subscribe(x => console.log(x));

Operators

Operators are methods on the Observable type that allow for composing asynchronous operations in a declarative manner. The code sample demonstrates the use of 'filter' and 'map' operators to process data.

const { of } = require('rxjs');
const { map, filter } = require('rxjs/operators');

const nums = of(1, 2, 3, 4, 5);
const squaredNums = nums.pipe(
  filter(n => n % 2 !== 0),
  map(n => n * n)
);
squaredNums.subscribe(x => console.log(x));

Handling Errors

This feature allows you to handle errors in an Observable sequence. The code sample demonstrates how to catch and handle errors using the 'catchError' operator.

const { throwError, of } = require('rxjs');
const { catchError } = require('rxjs/operators');

const observable = throwError(new Error('Something went wrong!'));
const handled = observable.pipe(
  catchError(error => of(`Caught: ${error.message}`))
);
handled.subscribe(x => console.log(x), err => console.error(err));

Combining Observables

This feature allows you to combine multiple Observables into one. The code sample demonstrates how to use 'combineLatest' to combine two streams of data.

const { combineLatest, of } = require('rxjs');

const temperature = of(70, 72, 76, 79, 75);
const humidity = of(40, 44, 49, 58, 55);

const combined = combineLatest([temperature, humidity]);
combined.subscribe(([temp, hum]) => console.log(`Temperature: ${temp} Humidity: ${hum}`));

Other packages similar to rxjs

most

Most.js is a high-performance reactive programming library. It offers similar functionality to RxJS but focuses on providing a smaller, faster, and more modular library.

xstream

XStream is a library for building asynchronous and event-based programs using observable streams. It is similar to RxJS but with a focus on simplicity and minimalism, offering a smaller set of operators.

kefir

Kefir.js is a Reactive Programming library with a focus on high performance and low memory usage. It is similar to RxJS but is more lightweight and has a slightly different API.

README

RxJS 5 (release candidate)

Reactive Extensions Library for JavaScript. This is a rewrite of Reactive-Extensions/RxJS and is intended to supersede it once this is ready. This rewrite is meant to have better performance, better modularity, better debuggable call stacks, while staying mostly backwards compatible, with some breaking changes that reduce the API surface.

Apache 2.0 License

• Code of Conduct
• Contribution Guidelines
• Maintainer Guidelines
• Creating Operators
• Migrating From RxJS 4 to RxJS 5
• API Documentation (WIP)

Important

By contributing or commenting on issues in this repository, whether you've read them or not, you're agreeing to the Contributor Code of Conduct. Much like traffic laws, ignorance doesn't grant you immunity.

Installation and Usage

ES6 via npm

npm install rxjs

To import the entire core set of functionality:

import Rx from 'rxjs/Rx';

Rx.Observable.of(1,2,3)

To import only what you need by patching (this is useful for size-sensitive bundling):

import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';

Observable.of(1,2,3).map(x => x + '!!!'); // etc

To import what you need and use it with proposed bind operator:

Note: This additional syntax requires transpiler support and this syntax may be completely withdrawn from TC39 without notice! Use at your own risk.

import { Observable } from 'rxjs/Observable';
import { of } from 'rxjs/observable/of';
import { map } from 'rxjs/operator/map';

Observable::of(1,2,3)::map(x => x + '!!!'); // etc

CommonJS via npm

npm install rxjs

Import all core functionality:

var Rx = require('rxjs/Rx');

Rx.Observable.of(1,2,3); // etc

Import only what you need and patch Observable (this is useful in size-sensitive bundling scenarios):

var Observable = require('rxjs/Observable').Observable;
// patch Observable with appropriate methods
require('rxjs/add/operator/map');

Observable.of(1,2,3).map(function (x) { return x + '!!!'; }); // etc

Import operators and use them manually you can do the following (this is also useful for bundling):

var Observable = require('rxjs/Observable').Observable;
var map = require('rxjs/operator/map').map;

map.call(Observable.of(1,2,3), function (x) { return x + '!!!'; });

You can also use the above method to build your own Observable and export it from your own module.

All Module Types (CJS/ES6/AMD/TypeScript) via npm

To install this library via npm version 3, use the following command:

npm install @reactivex/rxjs

If you are using npm version 2 before this library has achieved a stable version, you need to specify the library version explicitly:

npm install @reactivex/rxjs@5.0.0-rc.1

CDN

For CDN, you can use unpkg:

5.0.0-beta.1 - 5.0.0-beta.11:

https://unpkg.com/@reactivex/rxjs/dist/global/Rx.umd.js

5.0.0-beta.12 or higher:

https://unpkg.com/@reactivex/rxjs/dist/global/Rx.js

Node.js Usage:

var Rx = require('@reactivex/rxjs');

Rx.Observable.of('hello world')
  .subscribe(function(x) { console.log(x); });

Goals

• Provide better performance than preceding versions of RxJS
• To model/follow the Observable Spec Proposal to the observable.
• Provide more modular file structure in a variety of formats
• Provide more debuggable call stacks than preceding versions of RxJS

Building/Testing

The build and test structure is fairly primitive at the moment. There are various npm scripts that can be run:

• build_es6: Transpiles the TypeScript files from src/ to dist/es6
• build_cjs: Transpiles the ES6 files from dist/es6 to dist/cjs
• build_amd: Transpiles the ES6 files from dist/es6 to dist/amd
• build_global: Transpiles/Bundles the CommonJS files from dist/cjs to dist/global/Rx.js
• build_all: Performs all of the above in the proper order.
• build_test: builds ES6, then CommonJS, then runs the tests with jasmine
• build_perf: builds ES6, CommonJS, then global, then runs the performance tests with protractor
• build_docs: generates API documentation from dist/es6 to dist/docs
• build_cover: runs istanbul code coverage against test cases
• test: runs tests with jasmine, must have built prior to running.
• tests2png: generates PNG marble diagrams from test cases.

npm run info will list available script.

Example

# build all the things!
npm run build_all

Performance Tests

Run npm run build_perf or npm run perf to run the performance tests with protractor. Run npm run perf_micro to run micro performance test benchmarking operator.

Adding documentation

RxNext uses ESDoc to generate API documentation. Refer to ESDoc's documentation for syntax. Run npm run build_docs to generate.

Generating PNG marble diagrams

The script npm run tests2png requires some native packages installed locally: imagemagick, graphicsmagick, and ghostscript.

For Mac OS X with Homebrew:

• brew install imagemagick
• brew install graphicsmagick
• brew install ghostscript
• You may need to install the Ghostscript fonts manually:
  • Download the tarball from the gs-fonts project
  • mkdir -p /usr/local/share/ghostscript && tar zxvf /path/to/ghostscript-fonts.tar.gz -C /usr/local/share/ghostscript

For Debian Linux:

• sudo add-apt-repository ppa:dhor/myway
• apt-get install imagemagick
• apt-get install graphicsmagick
• apt-get install ghostscript

For Windows and other Operating Systems, check the download instructions here:

• http://imagemagick.org
• http://www.graphicsmagick.org
• http://www.ghostscript.com/