Hertha  Mayer

Hertha Mayer

1595341440

Understanding Observables in Angular

An Observable is like a data source. In an Angular project, it’s an object we import from a third-party package, rxjs. The observable here is implemented by following an _observable pattern _where we have an observable and an observer and in between, we have a timeline where we can have multiple events, or data packages, emitted by the observable (depending on the data source of the observable). These events can be triggered programmatically, by user interaction, like a button, HTTP requests, and dozens of other data sources.

The observer and handling the data

No, not the one from Fringe. Who or what is the observer then? It is actually our code, our “observing”, so to say, via a subscribe() function.

We have three ways of handling these packages. We can handle data, errors, or the completion of the observable, because these are the three types of data packages you can receive. It’s in these three that your code gets executed.

What should happen if I receive a data package? What should happen if there is an error or when the observable is completed?

Some observables are never done, like a button that can be clicked a bunch of times, others will resolve with the event (like an HTTP request). Generally, though, they are all used to handle async tasks. All these data sources triggered in your code are async tasks, you don’t know when they will happen or how long they will take and you don’t want to wait until the completion of these events blocking your other code. Historically you would use callbacks or promises, observables are just a different approach that is often the preferred way in Angular. Their major advantage is its operators, which we will talk more about later.

Let’s take a closer look

Observables are constructs to which you subscribe to see changes in data. Params is a good example:

ngOnInit() {
    this.route.params.subscribe((params: Params) => {
        this.userId = +params.userId
    })
}

Our params (of type Params) is a stream of route parameters that gives us a new param when we go to the next page and we subscribe to the userId in these params. It’s a stream of data that gives us new values. Angular uses observables heavily and all we have to do is subscribe to them, but it is good to know how they work, so let’s build our own observable.

It is worth noting that observables are not “baked into” JavaScrip or Typescript but rather managed by a package called**_ “rxjs”._**

Params is an observable object and Angular knows it. Any observable object can be subscribed to for changes with the subscribe() method.

Let’s build an observable that emits a new value every second and alerts it to the screen:

onClick() {
    interval(1000).subscribe(count => console.log(count))
}

let’s also attach it to a simple button which will trigger our listener when clicked, starting the counter:

<button (click)="onClick()">click me</button>

Now here is the thing. This particular observable will keep emitting values. Even if we switch to another site, it will keep printing an incrementing number to the console ad infinitum. Other observables might not necessarily act this way (like an HTTP request), and it is not always necessary to handle this behavior but in order to avoid memory leaks, it is a good practice to stop the observable when we are finished with it. We do that by storing our observable in a variable of the type Subscription and then by stopping it via the unsubscribe() method. Think of a Subscription as:

Subscription = Observable + subscribe()

#typescript #programming #javascript #javascript-tips #angular

What is GEEK

Buddha Community

Understanding Observables in Angular
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

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

Marcelle  Smith

Marcelle Smith

1592658821

Handling Observable in Angular using Async Pipe

Async pipe in angular helps in transforming data received asynchronously and when used along with an observable allows to:

  • Subscribe to the observable
  • Get its latest values
  • Marks it for onPush change detection
  • Automatically unsubscribes on destruction of the component

#angular 8 #angular app #angular route #angular services #observables

Roberta  Ward

Roberta Ward

1593184320

Basics of Angular: Part-1

What is Angular? What it does? How we implement it in a project? So, here are some basics of angular to let you learn more about angular.

Angular is a Typescript-based open-source front-end web application platform. The Angular Team at Google and a community of individuals and corporations lead it. Angular lets you extend HTML’s syntax to express your apps’ components clearly. The angular resolves challenges while developing a single page and cross-platform applications. So, here the meaning of the single-page applications in angular is that the index.html file serves the app. And, the index.html file links other files to it.

We build angular applications with basic concepts which are NgModules. It provides a compilation context for components. At the beginning of an angular project, the command-line interface provides a built-in component which is the root component. But, NgModule can add a number of additional components. These can be created through a template or loaded from a router. This is what a compilation context about.

What is a Component in Angular?

Components are key features in Angular. It controls a patch of the screen called a view. A couple of components that we create on our own helps to build a whole application. In the end, the root component or the app component holds our entire application. The component has its business logic that it does to support the view inside the class. The class interacts with the view through an API of properties and methods. All the components added by us in the application are not linked to the index.html. But, they link to the app.component.html through the selectors. A component can be a component and not only a typescript class by adding a decorator @Component. Then, for further access, a class can import it. The decorator contains some metadata like selector, template, and style. Here’s an example of how a component decorator looks like:

@Component({
    selector: 'app-root',
    templateUrl: 'app.component.html',
    styleUrls: ['app.component.scss']
})

Role of App Module

Modules are the package of functionalities of our app. It gives Angular the information about which features does my app has and what feature it uses. It is an empty Typescript class, but we transform it by adding a decorator @NgModule. So, we have four properties that we set up on the object pass to @NgModule. The four properties are declarations, imports, providers, and bootstrap. All the built-in new components add up to the declarations array in @NgModule.

@NgModule({
declarations: [
  AppComponent,
],
imports: [
  BrowserModule,
  HttpClientModule,
  AppRoutingModule,
  FormsModule
],
bootstrap: [AppComponent]
})

What is Data Binding?

Data Binding is the communication between the Typescript code of the component and the template. So, we have different kinds of data binding given below:

  • When there is a requirement to output data from our Typescript code in the HTML template. String interpolation handles this purpose like {{data}} in HTML file. Property Binding is also used for this purpose like [property] = “data”.
  • When we want to trigger any event like clicking a button. Event Binding works while we react to user events like (event) = “expression”.
  • When we can react to user events and output something at the same time. Two-way Binding is used like [(ngModel)] = “data”.

image for understanding data binding

#angular #javascript #tech blogs #user interface (ui) #angular #angular fundamentals #angular tutorial #basics of angular

Ayyaz Zafar

1624138795

Angular Material Autocomplete - Multiple Use Cases covered

Learn How to use Angular Material Autocomplete Suggestions Search Input. I covered multiple use cases.

Please watch this video. I hope this video would be helpful for you to understand it and use it in your projects

Please subscribe: https://www.youtube.com/channel/UCL5nKCmpReJZZMe9_bYR89w

#angular #angular-material #angular-js #autocomplete #angular-material-autocomplete #angular-tutorial