Reactive programming is a programming paradigm that deals with data streams and the propagation of change. This can be used to build asynchronous and event-based applications.
RxJS is a library for reactive programming using observables that makes it easy to work with asynchronous data streams.
In this post, we will learn about reactive programming with RxJS in JavaScript. We will cover the following topics:
Reactive programming is a programming paradigm that deals with data streams and the propagation of change.
In reactive programming, data is represented as a stream of values that can be processed over time. These values can be emitted by a source, such as a user input or a server response.
The stream of values can be transformed, combined, and filtered using operators. The output of the stream can be subscribed to and will be updated as the values in the stream change.
Reactive programming can be used to build asynchronous and event-based applications.
RxJS is a library for reactive programming using observables that makes it easy to work with asynchronous data streams.
RxJS provides an implementation of the Observer pattern. This pattern is used to subscribe to and receive notifications from a data source.
RxJS also provides a number of operators that can be used to transform, combine, and filter streams of values.
RxJS can be used in a number of ways. It can be used in the browser using a script tag, or it can be used in Node.js using the require() function.
It can also be used with a number of different module loaders, such as RequireJS, SystemJS, and Webpack.
RxJS observables can be created from a variety of data sources, such as arrays, Promises, and event emitters.
Observables can be created from scratch using the create() operator. This operator takes a function that is used to emit values from the observable.
const observable = Rx.Observable.create(function (observer) {
observer.next(1);
observer.next(2);
observer.next(3);
observer.complete();
});
Observables can be subscribed to using the subscribe() method. This method takes an observer object that defines the handlers for the next, error, and complete events.
observable.subscribe({
next: function (value) {
console.log(value);
},
error: function (error) {
console.log(error);
},
complete: function () {
console.log('complete');
}
});
Observables can be either hot or cold.
Hot observables are those that begin emitting values as soon as they are created. Cold observables are those that do not begin emitting values until they are subscribed to.
Subjects are a type of observable that can multicast to multiple observers. This means that a subject can be used to broadcast values to multiple observers.
Subjects can be created using the Subject class.
const subject = new Rx.Subject();
Subjects can be subscribed to in the same way as regular observables.
subject.subscribe({
next: function (value) {
console.log(value);
}
});
Subjects can also be used to emit values.
subject.next(1);
subject.next(2);
subject.next(3);
RxJS provides a number of operators that can be used to transform, combine, and filter streams of values.
Operators can be used with observables using the pipe() method.
const observable = Rx.Observable.create(function (observer) {
observer.next(1);
observer.next(2);
observer.next(3);
observer.complete();
}).pipe(
map(function (value) {
return value * 2;
}),
filter(function (value) {
return value > 2;
})
);
Errors can be handled using the catchError() operator. This operator takes a function that is used to handle errors.
const observable = Rx.Observable.create(function (observer) {
observer.next(1);
observer.next(2);
observer.next(3);
throw new Error('error');
}).pipe(
catchError(function (error) {
console.log(error);
})
);
This post only scratched the surface of what RxJS and reactive programming can do. For more information, check out the resources below.