Angular 4 Tutorial

Part-3 Angular Components

let's understand components in angular 4

getting started with angular

       
What we have done so far ?
This tutorial on angular 4 components is in continuation of our Angular 4 Tutorial Series and if you have not read the previous parts of the tutorial , it is recommended that you go through them first. In the last part , we learned about many important files and folders in Angular 4 and we'll refer to them again and again in this and further parts. If you want to go through them first , please use the following links.
  1. Part-1 :: Introduction
  2. Part-2 :: Angular 4 Project Structure
Angular 4 Components
Components are the cells or building blocks of an Angular app and when you're writing an angular 4 app , you'll spend a significant time creating and modifying components. Technically components are Typescript classes along with a component decorator where we provide metadata that dictates how the component should be used by the app. Note that in order to be usable in an angular 4 app , a component has to belong to a NgModule. In this part of the tutorial , we'll go back to our app.component.ts and explore its different parts and we'll also edit the component and add Inventions related information to the component. Let's get started.
How angular 4 component file looks like ?
Following is the code from our app.component.ts file , read the informative comments to see what's happening in each line.

// app.component.ts 
import { Component } from '@angular/core';  // import Component class from angular core 

// define the component metadata usnig the decorator and export the class so it can be 
// imported by other modules 
@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'app';
}

Now it's the time that we start getting our hands dirty in the code , let's start customizing this component as per our InventionsHub project. Let's add a new class to define an Invention , open your app.component.ts in your editor and make the changes mentioned below.

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

// add a new class 
export class Invention {
    name : String ; 
    inventor : String ; 
    year : String; 
}

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  // title = 'app';
  invention : Invention = {
      name : ' C Programming Language ' ,
      inventor : ' Dennis Ritchie ' , 
      year : ' 1972 '
  }
}


Good , so we created an Invention class and also initialized an object of the same in our app component , now we can go on and edit the template file app.component.html to bind this object to the view. Open the file app.component.html and make it look like the following snippet.

<!-- app.component.html -->

<div style="text-align:center">
    <h1>
        Welcome to {{title}}!!
    </h1>

</div>
<h2> Greatest Inventions in History of Mankind </h2>
<hr>

<!-- bind data using curly braces to the data in app.component.ts -->
<h2> {{ invention.name }} </h2>
<h3> {{ invention.inventor }} </h3>
<h3> {{ invention.year }} </h3>





Run your app
use command ng serve to run your app and it starts your app on http://localhost:4200

ng serve 
now point your browser to the above address and you should see something similar to the following screenshot.

Note that once you run ng serve , It will automatically reload your changes in the browser , you don't have to restart your project or reload your browser.
Summary
Wow! we've done it again, so in this part of our Angular 4 tutorial , we started exploring angular components
we also looked at a very basic example of data binding. In the next part of the tutorial , we'll learn how to create components. Hope you are enjoying learning about the angular 4 , see you in the next part.

       


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