Everything You Need to Know about Change Detection in Angular

If like me and want to have a comprehensive understanding of the change detection mechanism in Angular you’ll have to explore the sources since there is not much information available on the web. Most articles mention that each component has its own change detector which is responsible for checking the component, but they don’t go beyond that and mostly focus on use cases for immutables and change detection strategy. This article provides you with the information required to understand why use cases with immutables work and how change detection strategy affects the check. Also, what you will learn from this article will enable you to come up with various scenarios for performance optimization on your own.

This article consists of two parts. The first part is pretty technical and contains a lot of links to the sources. It explains in detail how the change detection mechanism works under the hood. Its content is based on the newest Angular version — 4.0.1. The way how change detection mechanism is implemented under the hood in this version is different from the earlier 2.4.1. If interested you can read a little about how it worked in this stackoverflow answer.

The second part shows how change detection can be used in the application and its content is applicable for both earlier 2.4.1 and the newest 4.0.1 versions of Angular since public API has not changed.

#angular #change-detection

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Everything You Need to Know about Change Detection in Angular

If like me and want to have a comprehensive understanding of the change detection mechanism in Angular you’ll have to explore the sources since there is not much information available on the web. Most articles mention that each component has its own change detector which is responsible for checking the component, but they don’t go beyond that and mostly focus on use cases for immutables and change detection strategy. This article provides you with the information required to understand why use cases with immutables work and how change detection strategy affects the check. Also, what you will learn from this article will enable you to come up with various scenarios for performance optimization on your own.

This article consists of two parts. The first part is pretty technical and contains a lot of links to the sources. It explains in detail how the change detection mechanism works under the hood. Its content is based on the newest Angular version — 4.0.1. The way how change detection mechanism is implemented under the hood in this version is different from the earlier 2.4.1. If interested you can read a little about how it worked in this stackoverflow answer.

The second part shows how change detection can be used in the application and its content is applicable for both earlier 2.4.1 and the newest 4.0.1 versions of Angular since public API has not changed.

#angular #change-detection

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!!!

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

· 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

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

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

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

Simplifying Angular Change Detection

Angular can detect when data changes in the component, and can re-render the view to display the updated data. Angular makes sure that data in the component and the view are always in sync with each other.

You must have used Angular bindings to display the data from the component or handle events raised on the view. Let us consider the next code listing:

@Component({
  selector: 'app-root',
  template: `
  <h2>{{count}}</h2>
  <button (click)='incCount()'>Increment</button>
  `
})
export class AppComponent implements OnInit {

  count: number = 10;
  incCount(): void{
    this.count = this.count +1; 
  }
  ngOnInit() {

  }

The above component uses interpolation and event binding to display data and call a function on the click event, respectively. Each time the button is clicked, the value of count increases by 1, and the view gets updated to display the updated data. So, here you can see that Angular can detect data changes in the component, and then automatically re-render the view to reflect the change.

The part of the Angular framework that does this is called the “change detector.” Every component has a change detector that reads the binding on the template and makes sure that the data model and view are in sync with each other. Whenever, for any reason (actually there are three reasons which we cover later in the article), data model changes, it is the change detector that projects the updated data to the view, so that the view and the data model are in sync with each other.

The syncing gets complex when the data model gets updated at runtime. Let’s take a look at the next code listing:

@Component({
  selector: 'app-root',
  template: `
  <h2>{{count}}</h2>
  `
})
export class AppComponent implements OnInit {

  count: number = 10;
  ngOnInit() {
    setInterval(() => {
      this.count = this.count + 1;
    },100)

  }
}

#angular #change detection #change detector tree #chagedetectorref #component

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”.

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

What every front-end developer should know about change detection in Angular and React.

In my pursuit to grow as a developer I spend a lot of time reverse-engineering web technologies. I’m basically a reverse-engineering addict. The topic that fascinates me the most is change detection. You can find this mechanism in almost any web application. It’s an integral part of the most popular web frameworks. Sufficiently advanced widgets, like datagrids or stateful jQuery plugins, have change detection. And there’s a good chance that change detection lurks somewhere in your application’s code base.

Every aspiring software architect must have a good understanding of this mechanism. I’d argue that change detection is the most important piece of an architecture since it’s responsible for the visible part like DOM updates. It’s also the area that significantly affects an application’s performance. This article will greatly expand your knowledge in this domain.

We’ll start by looking at the change detection in general. Then we’ll implement a very basic change detection mechanism ourselves. And once we’ve established the essence of change detection, we’ll take an in-depth look at how it’s implemented in Angular and React.

#angular #react #change-detection #reconciliation #frameworks