The Reactive Extensions for JavaScript...

...is a set of libraries to compose asynchronous and event-based programs using observable collections and LINQ-style query operators in JavaScript

This project has moved to CodePlex and only serves as a mirror.

About the Reactive Extensions

The Reactive Extensions for JavaScript (RxJS) is a set of libraries for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators in JavaScript. Using RxJS, developers represent asynchronous data streams with Observables, query asynchronous data streams using LINQ operators, and parameterize the concurrency in the asynchronous data streams using Schedulers. Simply put, RxJS = Observables + LINQ + Schedulers.

Whether you are authoring a web-based application in JavaScript or a server-side application in Node.js, you have to deal with asynchronous and event-based programming as a matter of course. Although some patterns are emerging such as the Promise pattern, handling exceptions, cancellation, and synchronization is difficult and error-prone.

Using RxJS, you can represent multiple asynchronous data streams (that come from diverse sources, e.g., stock quote, tweets, computer events, web service requests, etc.), and subscribe to the event stream using the Observer object. The Observable notifies the subscribed Observer instance whenever an event occurs.

Because observable sequences are data streams, you can query them using standard LINQ query operators implemented by the Observable type. Thus you can filter, project, aggregate, compose and perform time-based operations on multiple events easily by using these static LINQ operators. In addition, there are a number of other reactive stream specific operators that allow powerful queries to be written. Cancellation, exceptions, and synchronization are also handled gracefully by using the methods on the Observable object.

This set of libraries include:

• rx.js - Core library
• rx.modern.js - Core library for ES5 compliant browsers and runtimes
• rx.aggregates.js - aggregation event processing query operations
• rx.binding.js - binding operators including multicast, publish, publishLast, publishValue, and replay
• rx.coincidence.js - reactive coincidence join event processing query operations
• rx.experimental.js - experimental operators including imperative operators and forkJoin
• rx.joinpatterns.js - join patterns event processing query operations
• rx.testing.js - used to write unit tests for complex event processing queries.
• rx.time.js - time-based event processing query operations.

Why RxJS?

One question you may ask yourself, is why RxJS? What about Promises? Promises are good for solving asynchronous operations such as querying a service with an XMLHttpRequest, where the expected behavior is one value and then completion. The Reactive Extensions for JavaScript unifies both the world of Promises, callbacks as well as evented data such as DOM Input, Web Workers, Web Sockets. Once we have unified these concepts, this enables rich composition.

To give you an idea about rich composition, we can create an autocompletion service which takes the user input from a text input and then query a service, making sure not to flood the service with calls for every key stroke, but instead allow to go at a more natural pace.

Let's start with getting the user input from an input, listening to the keyup event.

/* Only get the value from each key up */
var keyups = Rx.Observable.fromEvent(input, 'keyup')
    .select(function (e) {
        return e.target.value;
    })
    .where(function (text) {
        return text.length > 2;
    });

/* Now throttle/debounce the input for 500ms */
var throttled = keyups
    .throttle(500 /* ms */);

/* Now get only distinct values, so we eliminate the arrows */
var distinct = keyups
    .distinctUntilChanged();

Now, let's query Wikipedia!

function searchWikipedia(term) {
    var url = 'http://en.wikipedia.org/w/api.php?action=opensearch'
        + '&format=json' 
        + '&search=' + encodeURI(term);
    return Rx.Observable.getJSONPRequest(url);
}

Once that is created, now we can tie together the distinct throttled input and then query the service. In this case, we'll call select to get the value, and then calling switchLatest to ensure that we're not introducing any out of order sequence calls. We'll filter the results to make sure we get values.

var suggestions = distinct
    .select(function (text) {
        return searchWikipedia(text);
    })
    .switchLatest()
    .where(function (data) {
        return data.length == 2 && data[1].length > 0;
    });

Finally, we call the subscribe method on our observable sequence to start pulling data.

suggestions.subscribe( function (data) {
    var results = data[1];
    /* Do something with the data like binding */
}, function (e) {
    /* handle any errors */
});

And there you have it!

API Documentation

Core:

• Observer
• Observable

Subjects:

• AsyncSubject
• BehaviorSubject
• ReplaySubject
• Subject

Schedulers:

• Scheduler object
• Scheduler.currentThread
• Scheduler.immediate
• Scheduler.timeout
• VirtualTimeScheduler

Disposables:

• CompositeDisposable
• Disposable
• RefCountDisposable
• SerialDisposable
• SingleAssignmentDisposable

Installation and Usage

There are multiple ways of getting started with the Reactive Extensions including:

In a Browser:

<script src="rx.js"></script>

Along with a number of our extras for RxJS:

<script src="rx.aggregates.js"></script>
<script src="rx.binding.js"></script>
<script src="rx.coincidencejs"></script>
<script src="rx.experimental.js"></script>
<script src="rx.joinpatterns.js"></script>
<script src="rx.testing.js"></script>
<script src="rx.time.js"></script>

Installing via NPM:

npm install rx
npm install -g rx

Using in Node.js:

var Rx = require('rx');

Installing all of RxJS via NuGet:

Install-Package RxJS-All

Or install via NuGet individual packages:

Install-Package RxJS-Main
Install-Package RxJS-Aggregates
Install-Package RxJS-Binding
Install-Package RxJS-Coincidence
Install-Package RxJS-Experimental
Install-Package RxJS-JoinPatterns
Install-Package RxJS-Testing
Install-Package RxJS-Time

Using RxJS with an AMD loader such as Require.js

require({
    'paths': {
        'rx': 'path/to/rx.js'
    }
},
['rx'], function(Rx) {
    var obs = Rx.Observable.returnValue(42);
    obs.subscribe(function (x) { console.log(x); });
});

Compatibility

RxJS has been thoroughly tested against all major browsers and supports IE6+, Chrome 4+, FireFox 1+, and Node.js v0.4+.

License

Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. Microsoft Open Technologies would like to thank its contributors, a list of whom are at http://rx.codeplex.com/wikipage?title=Contributors.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.