Sofia Kelly

Sofia Kelly

1566794521

Angular RxJS: Observables, Observers and Operators Introduction

In the above definition of RxJS, you have encountered the word reactive programming, so let me give you a brief example of reactive programming.

What Is Reactive Programming?

Reactive programming is a declarative programming paradigm concerned with the data streams and the propagations of change.

A programming paradigm is a style or way of programming.
Few common programming paradigms includes:

Imperative Programming

Control flow in imperative programming is explicit. Commands show how the computation takes place, step by step. Each step affects the global state of the computation.

Declarative Programming

Control flow in declarative programming is implicit. The programmer states only what the result should look like, not how to obtain it.

As RxJS is a declarative programming language, so for better understanding of this, let’s take a look at below example. I am going to show an example, how below code works in imperative and declarative programming both.

Example

For example: In imperative programming, a = b +c would mean that a is being assigned the result of b + c in the instant the expression is evaluated, and later, the values of b and c can be changed with no effect on the value of a.

On the other hand in reactive programming, which is declarative, the value of a is automatically updated whenever the value of b or c is changed, without the program having to re-execute the statement a = b + c to determine the presently assigned value of a.

So, RxJS is an incredible tool for reactive programming, and today we are going to dive a little deeper into what observables, observers and operators are.

What is an Observable?

An observable is just a function, which packs the data that can be passed around from one thread to another thread. They are created to emit the data synchronously or asynchronously based on their configuration. They are like the supplier of data to their consumer.

Angular use lot of observables in different scenarios. These includes:

  • To make AJAX request and response,Angular HTTP module uses observables.
  • Observables are used in Router and Form Modules to listen for and responds to user-inputs events.
  • The EventEmitter class extends Observable.

To better understand Observables, let’s create a sample code.

const GetSumObserver = {
	  sum: 0,
	  next(value) {
	    this.sum = this.sum + value;
	  },
	  error() { },        
	  complete() {
	    console.log('Total Sum: ' + this.sum);
	  }
	};
	 
	Rx.Observable.of(10, 20, 30) // Synchronously emits 10, 20, 30 and then completes.
	.subscribe(GetSumObserver);
	 
	// "Sum equals: 60"

sampleexample.ts

Here, in the above example, we have created our custom observable and subscribe it using the three input values, and the result should be the sum of all values passed to it.

What is an Observer?

In simple term, observers are the consumer of the data, which is emitted by observables as a producer. To consume data, observers subscribe to the observables using its subscribe() method. So, whenever observables emit data, all the registered observers received the data in next() callback.

An observer is an object that defines callback methods to handle three types of notifications that an observable can send. These callback methods are: next(), error() and complete().

  • To make AJAX request and response,Angular HTTP module uses observables.
  • Observables are used in Router and Form Modules to listen for and responds to user-inputs events.
  • The EventEmitter class extends Observable.

We have subscribed our observable using .subscribe() method using the .of() operator, passing the values as a parameter. Without subscribe calling, our observable will not emit any value.

What is an Operator?

RxJS provides us numerous operators like map(), filter(), concat() etc. to perform complex manipulation of the collection on the source observables. Operators are just like functions, which takes configuration options, and return a function that takes a source observable.

Few of the RxJS operators are:

  • To make AJAX request and response,Angular HTTP module uses observables.
  • Observables are used in Router and Form Modules to listen for and responds to user-inputs events.
  • The EventEmitter class extends Observable.

Let’s take a small example of operators.

Using pipe() operator, you can combine multiple operators. For example:

import { filter, map } from 'rxjs/operators';
	const squareOf2 = of(1, 2, 3, 4, 5,6)
	  .pipe(
	    filter(num => num % 2 === 0),
	    map(num => num * num)
	  );
	squareOf2.subscribe( (num) => console.log(num));

operators.ts

The of() method will create and return an Observable from the 1, 2, 3, 4, 5,6 numbers and the pipe() methodwill apply the filter() and map() operators on each emitted value.

Summary

In this blog, we read about observables, observers and operators used in Angular app. This post is not in details, but give you an overview of all these concepts. I shared links of few famous operators, which are frequently used in anyAngular app.

Further Reading

A comparison between Angular and React

Getting Started with Nx in Angular

Learn Angular 8 from Scratch for Beginners

Deploy an Angular app to Docker

CircleCI Test Configuration for Angular

Add Authentication to Your Angular PWA

AngularJS Directive with Example: ng-init, ng-app, ng-repeat, ng-model

What’s the difference between AngularJS and Angular?

Top 18 Mistakes AngularJS Developers Makes

In the above definition of RxJS, you have encountered the word reactive programming, so let me give you a brief example of reactive programming.

What Is Reactive Programming?

Reactive programming is a declarative programming paradigm concerned with the data streams and the propagations of change.

A programming paradigm is a style or way of programming.
Few common programming paradigms includes:

Imperative Programming

Control flow in imperative programming is explicit. Commands show how the computation takes place, step by step. Each step affects the global state of the computation.

Declarative Programming

Control flow in declarative programming is implicit. The programmer states only what the result should look like, not how to obtain it.

As RxJS is a declarative programming language, so for better understanding of this, let’s take a look at below example. I am going to show an example, how below code works in imperative and declarative programming both.

Example

For example: In imperative programming, a = b +c would mean that a is being assigned the result of b + c in the instant the expression is evaluated, and later, the values of b and c can be changed with no effect on the value of a.

On the other hand in reactive programming, which is declarative, the value of a is automatically updated whenever the value of b or c is changed, without the program having to re-execute the statement a = b + c to determine the presently assigned value of a.

So, RxJS is an incredible tool for reactive programming, and today we are going to dive a little deeper into what observables, observers and operators are.

What is an Observable?

An observable is just a function, which packs the data that can be passed around from one thread to another thread. They are created to emit the data synchronously or asynchronously based on their configuration. They are like the supplier of data to their consumer.

Angular use lot of observables in different scenarios. These includes:

  • To make AJAX request and response,Angular HTTP module uses observables.
  • Observables are used in Router and Form Modules to listen for and responds to user-inputs events.
  • The EventEmitter class extends Observable.

To better understand Observables, let’s create a sample code.

const GetSumObserver = {
	  sum: 0,
	  next(value) {
	    this.sum = this.sum + value;
	  },
	  error() { },        
	  complete() {
	    console.log('Total Sum: ' + this.sum);
	  }
	};
	 
	Rx.Observable.of(10, 20, 30) // Synchronously emits 10, 20, 30 and then completes.
	.subscribe(GetSumObserver);
	 
	// "Sum equals: 60"

sampleexample.ts

Here, in the above example, we have created our custom observable and subscribe it using the three input values, and the result should be the sum of all values passed to it.

What is an Observer?

In simple term, observers are the consumer of the data, which is emitted by observables as a producer. To consume data, observers subscribe to the observables using its subscribe() method. So, whenever observables emit data, all the registered observers received the data in next() callback.

An observer is an object that defines callback methods to handle three types of notifications that an observable can send. These callback methods are: next(), error() and complete().

  • To make AJAX request and response,Angular HTTP module uses observables.
  • Observables are used in Router and Form Modules to listen for and responds to user-inputs events.
  • The EventEmitter class extends Observable.

We have subscribed our observable using .subscribe() method using the .of() operator, passing the values as a parameter. Without subscribe calling, our observable will not emit any value.

What is an Operator?

RxJS provides us numerous operators like map(), filter(), concat() etc. to perform complex manipulation of the collection on the source observables. Operators are just like functions, which takes configuration options, and return a function that takes a source observable.

Few of the RxJS operators are:

  • To make AJAX request and response,Angular HTTP module uses observables.
  • Observables are used in Router and Form Modules to listen for and responds to user-inputs events.
  • The EventEmitter class extends Observable.

Let’s take a small example of operators.

Using pipe() operator, you can combine multiple operators. For example:

import { filter, map } from 'rxjs/operators';
	const squareOf2 = of(1, 2, 3, 4, 5,6)
	  .pipe(
	    filter(num => num % 2 === 0),
	    map(num => num * num)
	  );
	squareOf2.subscribe( (num) => console.log(num));

operators.ts

The of() method will create and return an Observable from the 1, 2, 3, 4, 5,6 numbers and the pipe() methodwill apply the filter() and map() operators on each emitted value.

Summary

In this blog, we read about observables, observers and operators used in Angular app. This post is not in details, but give you an overview of all these concepts. I shared links of few famous operators, which are frequently used in anyAngular app.

Further Reading

A comparison between Angular and React

Getting Started with Nx in Angular

Learn Angular 8 from Scratch for Beginners

Deploy an Angular app to Docker

CircleCI Test Configuration for Angular

Add Authentication to Your Angular PWA

AngularJS Directive with Example: ng-init, ng-app, ng-repeat, ng-model

What’s the difference between AngularJS and Angular?

Top 18 Mistakes AngularJS Developers Makes

#angular

What is GEEK

Buddha Community

Angular  RxJS: Observables, Observers and Operators Introduction
Christa  Stehr

Christa Stehr

1598940617

Install Angular - Angular Environment Setup Process

Angular is a TypeScript based framework that works in synchronization with HTML, CSS, and JavaScript. To work with angular, domain knowledge of these 3 is required.

  1. Installing Node.js and npm
  2. Installing Angular CLI
  3. Creating workspace
  4. Deploying your First App

In this article, you will get to know about the Angular Environment setup process. After reading this article, you will be able to install, setup, create, and launch your own application in Angular. So let’s start!!!

Angular environment setup

Install Angular in Easy Steps

For Installing Angular on your Machine, there are 2 prerequisites:

  • Node.js
  • npm Package Manager
Node.js

First you need to have Node.js installed as Angular require current, active LTS or maintenance LTS version of Node.js

Download and Install Node.js version suitable for your machine’s operating system.

Npm Package Manager

Angular, Angular CLI and Angular applications are dependent on npm packages. By installing Node.js, you have automatically installed the npm Package manager which will be the base for installing angular in your system. To check the presence of npm client and Angular version check of npm client, run this command:

  1. npm -v

Installing Angular CLI

  • Open Terminal/Command Prompt
  • To install Angular CLI, run the below command:
  1. npm install -g @angular/cli

installing angular CLI

· After executing the command, Angular CLI will get installed within some time. You can check it using the following command

  1. ng --version

Workspace Creation

Now as your Angular CLI is installed, you need to create a workspace to work upon your application. Methods for it are:

  • Using CLI
  • Using Visual Studio Code
1. Using CLI

To create a workspace:

  • Navigate to the desired directory where you want to create your workspace using cd command in the Terminal/Command prompt
  • Then in the directory write this command on your terminal and provide the name of the app which you want to create. In my case I have mentioned DataFlair:
  1. Ng new YourAppName

create angular workspace

  • After running this command, it will prompt you to select from various options about the CSS and other functionalities.

angular CSS options

  • To leave everything to default, simply press the Enter or the Return key.

angular setup

#angular tutorials #angular cli install #angular environment setup #angular version check #download angular #install angular #install angular cli

Cómo Usar El Operador SwitchMap En RxJS En angular

Tutorial sobre el uso del operador switchMap en #RxJS (ReactiveX) en #Angular. Dura más de lo habitual debido a que lo explicamos con dos ejemplos, uno muy básico y uno de los típicamente llamados "Ejemplo de la Vida Real" (Real life example). Para ver los puntos más importantes, les dejamos los siguientes minutos:

#rxjs #angular 

Sasha  Roberts

Sasha Roberts

1626834660

Angular Rxjs: Use .map() And Async Pipe (Refactor Your Code)

In this video, we will see how to improve our code using the #rxs map operator and #angular #async pipe.

The components should be clean and minimal and should not have code that manipulates the data. Responsible for data manipulation is a service.
The goal is to prepare our data and return an #observable pipe so that we can use an #async pipe in the template.

code: https://github.com/profanis/codeShotsWithProfanis/tree/13/rxjsMapAndAsyncPipe

#angular #rxjs #observable #map #async

#angular rxjs #angular #angular tutorial #what is angular

Rupert  Beatty

Rupert Beatty

1616102700

Angular Meets RxJS: RxJS Operators

Introduction

This article belongs to a series called “Angular meets RxJS” in which I try to explain reactive programming using “RxJS” in an “Angular” context the best I can.

Table of contents

Basic concepts

RxJS subjects

RxJS operators (Part 1)

RxJS operators (Part 2)

RxJS operators (Part 3)

“takeUntil” and the “async” pipe

Higher-order observables

Error handling

RxJS schedulers (coming soon)

Mini-project: Build a Pokedex (coming soon)

In the previous article…

…we talked about functional programming, marble diagrams and creation operators. We used them to create observables out of regular values or by combining other observables. Now, we’re going to see the other type of operators: the pipeable ones. These operators are used to transform an observable into another one.

There are more than a hundred of operators so it’s obvious that I won’t talk about all of them. Indeed, I’ll focus on the most popular and useful ones. However, if you have any question or if you think that I forgot an important one, please tell me in the comments and I’ll update the article.

#angular #reactive-programming #observables #javascript #rxjs

Clara  Gutmann

Clara Gutmann

1599164940

Angular Observables: How to Use Observables In Angular

Angular Observables provide the support for passing the messages between publishers(Creator of Observables) and subscribers(User of Observables) in your application. Observables are declarative that is, you define the function for publishing values, but it is not executed until the consumer subscribes to it. We have already covered the  Angular 9 Tutorial on this blog.

The observable can deliver the multiple values of any type like literals, messages, or events, depending on the context. As a publisher, you can create an Observable instance that defines a subscriber function. This is a function that is executed when the consumer calls the subscribe() method.

Define Angular Observers

The handler for receiving the observable notifications implements the Observer interface. It is an object that defines the callback methods to handle the three types of notifications that an observable can send. These are the following.

  1. next: Required. The handler for each delivered value called zero or more times after execution starts.
  2. error: Optional. The handler for error notification. The error halts the execution of the observable instance.
  3. complete: Optional. The handler for an execution-complete notification. The delayed values can continue to be delivered to a next handler after execution is complete.

#angular #angular observables #angular 9