Nico Jonsson

Nico Jonsson

1587354752

Difference between Constructor and NgOnInit in Angular

ngOnInit and constructor methods in Angular might be confusing to you,if you are new to Angular.In this tutorial, we will cover the differences between ngOnInitconstructor.

What is a Constructor?

A constructor is a special method which will be called whenever we create new objects. And generally used of initializing the class members. It is a feature of the class(typescript) itself, an object-oriented design concept not Angular.

If you are coming from the object-oriented programming background, you will know what exactly is a constructor & what it will do.

Have a look at the below typescript class example to understand constructor

class AddNumbers{
     x: number;
     y: number;
     constructor(x: number, y: number) {
        this.x = x;
        this.y = y;
     }
     add() {
      return this.x+this.y;
     }
}

The above class will be translated to JavaScript function

var AddNumbers= (function () {
    function AddNumbers(x, y) {
        this.x = x;
        this.y = y;
    }
    AddNumbers.prototype.add = function () {
      return this.x + point.x;
    };
    return AddNumbers;
})();

var numbers = new AddNumbers(2,4);
var additionOfNumbers = numbers.add();
console.log(additionOfNumbers); //Prints 6

If you see the above example constructor will be automatically invoked by JavaScript engine when we create a new object. Whereas add() method is being added to the prototype of the class.

We will call it whenever it is required. Our ngOnInit() method is just a method being added to the prototype of the class. We will take an angular component example to understand it further.

What is ngOnInit() in Angular?

  1. ngOnInit is a life cycle hook managed by Angular
  2. ngOnInit being added to prototype of the class created
  3. ngOnInit called by Angular when component is initialized
  4. Actual business logic performed ngOnInit method

Every component we create has a life cycle managed by Angular.

As part of the life cycle, angular creates it, renders it and checks when its bounded data properties changes, destroys the component before removing it from the DOM.

Angular exposes few lifecycle hooks that gives visibility into this events and to do post initialization operations when they occur.

One of the lifecycle hooks is ngOnInit()

ngOnInit() called by Angular to indicate that Angular is done with initializing the component.

To use ngOnInit() we have to import OnInit from @angular/core (Actually it is not required but as a good practice import the OnInit)

Whenever you create a new component using angular-cli ngOnInit being added by default.

Go through the sample example

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

@Component({
selector:'app-checkbox',
templateUrl:'./checkbox.component.html',
styleUrls: ['./checkbox.component.css']
})

export class CheckboxComponent implements OnInit {
constructor() {
console.log('Called Constructor');
}

ngOnInit() {
console.log('Called ngOnInit method');
}

}

This will be transformed the below Javascript function

var CheckboxComponent = /** @class */ (function () {

function CheckboxComponent() {
}

CheckboxComponent.prototype.ngOnInit=function () {
};

CheckboxComponent=__decorate([

Object(_angular_core__WEBPACK_IMPORTED_MODULE_0__["Component"])({
selector:'app-checkbox',
template:
__webpack_require__(/*! ./checkbox.component.html */"./src/app/checkbox/checkbox.component.html"),
styles:
[__webpack_require__(/*! ./checkbox.component.css */"./src/app/checkbox/checkbox.component.css")]
}),
__metadata("design:paramtypes", [])],
CheckboxComponent);

return CheckboxComponent;
}());

ngOnInit() method is added to the prototype of the checkbox component function.

That means someone has to invoke it, whereas constructor is automatically called by JavaScript engine. And this method is called Angular when the component is rendered.

That means somewhere in the angular core checkboxcomponent.ngOnInit() will be called when it finishes rendering the component.

When is ngOnInit Executed?

  1. ngOnInit will be executed, When Angular done with the creating of component DOM.
  2. ngOnInit will be called after the constructor execution and after first ngOnChanges

To understand it further will take an example

Understand difference between constructor & ngOnInit() in Angular with example

We will take an example of the Angular Material Checkbox component.

I have created a checkbox list component which displays two material checkboxes using a child component 

import { Component, OnInit } from '@angular/core';
import { Component, OnInit } from '@angular/core';
import { checkboxInformation } from '../checkboxInformation';
@Component({
selector: 'app-checkboxlist',
templateUrl: './checkboxlist.component.html',
styleUrls: ['./checkboxlist.component.css']
})
export class CheckboxlistComponent implements OnInit {

checkboxes : checkboxInformation[]=
[new checkboxInformation(true,"Angular Material Checkbox Checked"),
new checkboxInformation(false,"Angular Material Checkbox UnChecked")];

constructor() { }
ngOnInit() {}
}

//checkboxlist.component.html
<div>
<app-checkbox *ngFor="let item of checkboxes" [checkboxInfo]="item"></app-checkbox>
</div>

And the child component is

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

@Component({
selector: 'app-checkbox',
templateUrl: './checkbox.component.html',
styleUrls: ['./checkbox.component.css']
})

export class CheckboxComponent implements OnInit {

@Input() checkboxInfo : checkboxInformation; 

constructor() { 
console.log('Called Constructor method');
console.log(this.checkboxInfo);
//Displays undefined
}

ngOnInit() {
console.log('Called ngOnInit method');
console.log(this.checkboxInfo);
}
}

// And checkbox.component.html file is 
<p><mat-checkbox [(checked)]="checkboxInfo.status">
{{checkboxInfo.label}}</mat-checkbox></p>

And in addition to it, I have created a class checkboxInformation

export class checkboxInformation{
    label:string;
    status:boolean;
    constructor(_enabled : boolean, _label :string ){
       this.label = _label;
       this.status = _enabled;
   }
}

The output is

This is image title

Constructor vs ngOnInit Difference example

Here I am using @Input Decorator to pass value from parent component  CheckboxlistComponent  to child component CheckboxComponent

@Input property is not initialized until the component view is set up. Which will not happen at the time of constructor invocation, that is why if I try to access the @Input property checkboxInfo in constructor  console.log(this.checkboxInfo)

It will be displayed as undefined

ngOnInit() is invoked when everything in the component is initialized. So that is why checkboxInfo value is available inside the ngOnInit() method.

In other words, The ngOnInit() lifecycle hook Initialize the component after Angular first displays the data-bound properties and sets the component’s input properties It is a guarantee that our bindings are readily available.

It is called only once.

When to use constructor & when to use ngOnInit in Angular

In object-oriented programming, world constructor is used to initialize the class members and used for dependency injection.

Constructor usage in Angular

In Angular, the constructor is used for injecting dependencies into the component class. Nothing much. And keep the constructor as simple as possible. Unit testing can be very easy if the constructor logic is simple.

ngOnInit() method usage in Angular

As explained above Angular calls ngOnInit when it finishes creating a component DOM. And we will use constructors to inject all required dependencies and processed input bindings.

So we have everything in place so put actual logic in ngOnInit() method.

It’s a common practice to use ngOnInit to do actual work even though the logic doesn’t depend on DI, DOM or input bindings.

ngOnInit vs Constructor in Angular

This is image title

The difference was so simple.

I hope you understand all the differences between constructor and ngOnInit method in Angular.

Thank you!

#angular #javascript #coding

What is GEEK

Buddha Community

Difference between Constructor and NgOnInit 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

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

Why the industries are choosing to react instead of angular - INFO AT ONE

Angular JS is a typescript-based application developed by Google. It’s an open-source web application framework, specifically made for the front end Web developers. As we know that the Angular is created by Google it gets very good support from Google and some individual communities of developers.

Read More:- https://infoatone.com/why-the-industries-are-choosing-to-react-instead-of-angular/

#angular #angular and react #js cons of angular #cons of react js #difference between angular and react js #pros of react js