Sintek Ong

Sintek Ong

1565751859

How Change Detection Works In Angular

Originally published by Adesh at zeptobook.com

Today I would like to discuss about change detection in Angular. Change detection is crucial to understand in order to keep Angular application’s performance better. In a small Angular application, you will not see any significant performance boost using change detection. But, in larger applications having thousands of components with complex component tree structure, will have performance boost using change detection.

What is change detection in Angular?

Change Detection means updating the DOM whenever data is changed. Angular can detect when component data changes, and then automatically re-render the view to reflect that change.

Any component’s state change is triggered by these three things:-

  • Events – click, submit….
  • HTTP API – any interaction with server
  • Timers – setTimeout(), setInterval()

There need to be a mechanism to detect component state changes, and re-rendered the view as needed. Here is where change detection comes into play.

Angular Default Change Detection Strategy

By default Angular uses the ChangeDetectionStrategy.Default change detection strategy.

The default strategy of change detection in Angular starts at the top at its root component and goes down the component tree, checking every component even if it has not changed. It compares the current value of the property used in the template expression with the previous value of that property.

Let’s have a look at our user component.

import { Component, OnInit, Input } from '@angular/core';

@Component({
selector: ‘app-user’,
templateUrl: ‘./user.component.html’,
styleUrls: [‘./user.component.css’]
})
export class UserComponent implements OnInit {

@Input() user;

ngOnInit() { }

get runChangeDetection() {
console.log(‘Running change detection’);
return true;
}
}


<h2>
Hello {{user.firstname}} {{user.lastname}} !
</h2>
{{runChangeDetection}}

Place this user component inside the app component. Here is our app component.

<app-user [user]=‘admin’></app-user>
<button (click)=‘changeName()’>Change Name</button>


import { Component, OnInit } from ‘@angular/core’;

@Component({
selector: ‘app-root’,
templateUrl: ‘./app.component.html’,
styleUrls: [‘./app.component.css’]
})
export class AppComponent implements OnInit {
admin: any;

ngOnInit() {
this.admin = {
firstname: ‘James’,
lastname: ‘Copper’
};
}

changeName() {
this.admin.firstname = ‘Nicole’;
}
}

Let me walk through the above code. In the above code, I have created a simple user component with a @Input()parameter user, and a method runChangeDetection().

In the app component, I have placed this user component as a child component and setting the user attribute of <app-user></app-user> to admin object of app component. There is a button, where we are changing the firstname of admin object on its click event.

As soon as we click the button, and change the property of our admin object, Angular will trigger the change detection to make sure the DOM is sync with the object, which is admin in this case. For each property changes, Angular change detector will traverse the component tree and update the DOM.

On every click, there is a console log like below:-

Now, as you see, every time you change the object property, Angular will trigger change detection. As a result, change detector will traverse through the whole component tree, starting from root to the bottom. Traversing and change detection is a heavy process, which may cause performance degradation of application.

What if, we have thousands of components in tree, and even a single change in object property trigger the change detection. Then change detector has to traverse all those thousands components in tree in order to make DOM updated as required. This may lead to performance problem.

Although Angular is very fast, as your app grows, Angular will have to work harder to keep track of all the changes. What if we could help Angular and give it a better indication of when to check our components?

OnPush Change Detection Strategy

Angular offers another change detection strategy: it’s called OnPushand it can be defined on any component.

With this strategy, the template of the component will only be checked in 2 cases:

  • one of the inputs of the component changed (to be more accurate, when the reference of one of the inputs changes);
  • an event handler of the component was triggered.

This can be very convenient when the template of a component only depends on its inputs, and can give a serious boost to your application.

We can set the ChangeDetectionStrategy of our component to ChangeDetectionStrategy.OnPush

Let’s get back to our <app-user> component, and see how to implement OnPush change detection. This is very simple and straight forward step.

import { Component, OnInit, Input, ChangeDetectionStrategy } from ‘@angular/core’;

@Component({
selector: ‘app-user’,
templateUrl: ‘./user.component.html’,
styleUrls: [‘./user.component.css’],
changeDetection: ChangeDetectionStrategy.OnPush
})
export class UserComponent implements OnInit {

@Input() user;

ngOnInit() { }

get runChangeDetection() {
console.log(‘Running change detection from user component’);
return true;
}
}

I have added changeDetection to onPush on line 7, keep rest of the code same. Now, click on button and see the effects.

There is no name change and no console log as well. You might be wondering, why this is not happening. The reason being is that, on implementing the onPush change detection, Angular will run the change detector only when the reference passed to the component is changed instead of some property changed in the object.

So, here in our previous code in app component changeName() event, we are just changing the object property, not changing the reference.

this.admin.firstname = ‘Nicole’;

So, as per onPush strategy, it will not trigger the change detection, and no DOM will be updated. To fix this issue, we have to change our code like below:

changeName() {
this.admin = {
firstname: ‘Nicole’,
lastname: ‘Kooper’
};
}

In the above code snippet, we are changing the reference of the object instead of just changing just one property. Now when you run the application, you will find on the click of the button that the DOM is being updated with the new value.

Summary

In this blog, we learned about basics of Angular change detection and how can we accomplish it in our components. OnPush change detection strategy can boost performance of any large scale application. In the upcoming posts, I will try to cover other aspects of Change detection as well.

Originally published by Adesh at zeptobook.com

==========================================

Thanks for reading :heart: If you liked this post, share it with all of your programming buddies! Follow me on Facebook | Twitter

Learn More

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☞ Complete Angular 8 from Zero to Hero | Get Hired

☞ Learn and Understand AngularJS

☞ The Complete Angular Course: Beginner to Advanced

☞ Angular Crash Course for Busy Developers

☞ Angular Essentials (Angular 2+ with TypeScript)

☞ Angular (Full App) with Angular Material, Angularfire & NgRx

☞ Angular & NodeJS - The MEAN Stack Guide

#angular #web-development

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Buddha Community

How Change Detection Works 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

Turner  Crona

Turner Crona

1595865120

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

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

Mansi Gandhi

Mansi Gandhi

1625232772

Why Choose AngularJS framework for the enterprise? | Angular development Company - CMARIX

Although Angular JS has bought headlines over the domain of Web application development, its relevance downtime does not offer any guarantee. Since the JavaScript application is the child of Google, its web features may have some value. Angular JS enables the developer to write most of the code in HTML which brings the application together. Such potentiality and simplicity of the program from the Angular Development Company made Angular popular among JavaScripts.

But the real question arises on the integrity and the safety Angular can provide to the industry. Angular regularly updates its libraries to fix security issues over earlier versions. However, the private and customized Angular versions fall back from the latest versions. These versions might lack the crucial security patches. As a piece of advice, developers can share their improvement requests in the community.

Backward compatibility indicates that the updated versions can function with the outdated versions. Hence, it can simplify the migration procedures to the latest Angular version. Some portions of the AngularJS apps need lazy loading to ease the update and to facilitate the transfer of large projects.

Since AngularJS tends to spoil backward compatibility, it might cause future problems in a program.

The Changing Face of Frameworks

There were several ups and downs in the Web application market over the past. A few years ago, SproutCore ruled the throne as a top framework. However, according to Google search trends, BackboneJS later stole the spotlight which again passed over to EmberJS. But, there remains no comparison for AngularJS.

Birthed by Adam Abrons and Misko Hevery, the Brat Tech engineers in 2009, the Angular Development Company AngularJS took a swift transition to open-source. When Misko Hevery joined Google, he continued to develop Angular JS. The platform began to earn its place by December of 2012 according to Google Trends.

In the year 2015, the potential of AngularJS surpassed other frameworks and offered job placements for many developers. However, AngularJS is not entirely without competition as Facebook came up with ReactJS. Hence, there is a race to show which surpasses the other. But, according to Jeff Schroeder, among the native apps, React elevates mobile app development to higher levels.

Continuous Development in Angular JS

AngularJS has high popularity yet, the developers break backward compatibility on a regular basis. Therefore, the supporters of AngularJS have to learn the AngularJS framework again and again. A critic of AngularJS – Danny Tuppeny, points out that the framework is unstable as it offers short-term support. The developers develop the framework every now and then which can puzzle its users. However, a mobile Web developer by the name of Nene Bodonkor indicates another factor. The frameworks become satisfactory and since they fail to keep up with the market requirements, change becomes crucial.

On the contrary, Yehuda Katz, the creator of EmberJS suggests that the fast-paced lifestyle needs to slow down. Therefore, these constant changes can compel people to reduce and balance their pace. Both, ReactJS from Facebook and EmberJS fight to achieve maximum backward compatibility. Such a characteristic helps these frameworks to come to use for an enterprise. But, AngularJS still has its upper hand over its competitors.

The simple-to-learn design of the Angular Framework with various functions

A legacy system includes few characteristics like old technology that are not compatible with the present systems. These systems do not remain available for purchase from distributors or vendors. These legacy systems cannot update nor patch up by themselves as the developer or vendor stops its maintenance.

The CTO of a mobile and Web app development company Monsoon, Michi Kono agreed on the decisions. But he also commented that the core developers at AngularJS miscommunicated the information. As the AngularJS framework has its uses in Google, they can use the platform for legacy versions and supporting enterprises. According to Michi Kono, AngularJS can promise a safe approach for its use in enterprises. The framework of Angular Development Company USA makes learning simple as it lacks strong convention opinions. The framework is easy for developers to learn and Angular has its applications on other parallel technologies. Vast organizations that have a demand for on-scale development and hiring procedures can use the framework to their advantage.

The low level of Angular appears more as a toolbox than a framework. Such an approach makes Angular useful on a wide variety of utility functions. The developer can use the JavaScript framework to add a single website button through a separate framework. Major companies like Google, Facebook and Microsoft aim to improve JavaScript to match entrepreneur requirements. Since AtScript or the typed JavaScript from Google, will form the backbone of AngularJS 2.0, several developers shall prefer to leverage it.

The Best Fit

AngularJS has several promising aspects for developers from different enterprises to try. But the JavaScript framework undergoes several alterations by its developers. Yet, some of the JavaScript frameworks grab the focus of various users for which they remain in maintenance. Therefore, according to Brian Leroux, the Adobe Web developer, there are two options left. Developers can either imprison themselves within vast rewrites with no forward progress. Or Hire angular developers who can focus their attention to optimize the website architecture. Therefore, developers need to stay up-to-date with the current developments in the web application frameworks like AngularJS.

AngularJS frameworks carry lots of potential in real-time markets. But, the developers need to stay up-to-date to tackle the regular changes in its infrastructure.

#hire angular developers #angular #angular web development #angular development company #angular services #angularjs