Skip to main content

Component in Angular

Component in Angular

A component is a basic building block of UI in an Angular. it controls on UI of application. it is easily reusable.
or we can say Components are defined using the @component decorator. A component has a selector, template, style, and other properties, using which it specifies the metadata required to process the component.
How to create Component
we have angular CLI command of creating an angular component
ng generate component component-name
in short form, we can write it as
ng g c component-name

once you hit this command below file will add inside the component directory

  • HTML: it defines user interface which contains HTML/View of Application, directive & data binding
  • CSS: it has the style of the respective component
  • TS: (it is typescript file, we have to import component class inside TS file, it has class, decorator)
  • Spec: The spec files are unit tests for your source files. The convention for Angular applications is to have a .spec.ts file for each .ts file. They are run using the Jasmine javascript test framework through the Karma test runner when you use the ng test command.
now comes on TS file which has import, decorator, export, class keyword what are they?
  1. import component class from the angular library.

     import { Component, OnInit } from '@angular/core';
  1. decorator: here decorator denoted by @ & decorator name is Component, decorator is a function we can pass object as parameters. it metadata that has extra information of data.

    @Component({
  selector: 'app-questions-view',
  templateUrl: './questions-view.component.html',
  styleUrls: ['./questions-view.component.scss']
    })
we have below metadata
selector: A CSS selector that tells Angular to create and insert an instance of this
component wherever it finds the corresponding tag in template HTML. For example, if an app’s HTML contains <app-questions-view></app-questions-view>,
then Angular inserts an instance of the QuestionsViewComponent view between those tags.
-Template: inline HTML
-template URL: define path of external HTML
-Style: Inline CSS
-styleStyleURL: define Path of external css

3.class: class is typescript function or object inside we do coding, data binding, methods.

    export class QuestionsViewComponent implements OnInit {
     questionOne: string = "what is component in Angular"
      constructor() { }

      ngOnInit() {
  }

     }

Comments

Post a Comment

Popular

JavaScript type hoisting with variable function Expression

JavaScript type hoisting with variable function Expression Hoisting is JavaScript default behavior to moving declaration on the top. Variable can be used before its declaration. To understand this, first we need to understand of hoist meaning, hoist means “raise(something) by means of ropes & pulleys”. now we can relate hoisting with JavaScript. JavaScript interpreter moves all declaration on the top at runtime. It is best practice to declare all variable at the top of their respective scopes. , JavaScript is loosely syntax language so it will not throw any error at runtime if the variable used before its declaration. But JavaScript does not allow variable used before its declaration in “use strict” mode. Example 1 In this example, we can see in a normal scenario, when y has declared & then used. in this case, it will give output 10 as excepted. <p id= "demo" ></p> <script> var y; //Declare y y = 10 ; ...
4 comments
Read more

Life cycle hook

In Angular, every component has a life-cycle, a number of different stages it goes through. Creates the component Renders the component Creates and renders the component children Checks when the component data-bound properties change, and  Destroys the component before removing it from the DOM ngOnChanges this method is called  once  on component’s creation and then  every time changes  are detected in one of the component’s  input  properties. export class MyComponent implements OnChanges { ngOnChanges(changes: SimpleChanges) { // Insert Logic Here! } }   ngOnInit Invoked when given component has been initialized. This hook is only called  once  after the first  ngOnChanges export class MyComponent implements OnInit { ngOnInit() { // Insert Logic Here! } }     ngDoCheck Invoked when the change detector of the given component is invoked. It allows us to implement our own chang...
Post a Comment
Read more

DOM(Document Object Model) and BOM(Browser Object Model)

DOM(Document Object Model) The DOM is the Document Object Model, which deals with the document, the HTML elements themselves, It organize the elements of the document in tree structure (DOM tree) and in the DOM tree, all elements of the document are defined as objects (tree nodes) which have properties and methods.When a web page is loaded, the browser creates a DOM tree for all the objects (Html elements) of that page. e.g. document and all traversal you would do in it, events, etc. A Simple DOM Tree BOM(Browser Object Model) The BOM is the Browser Object Model, which deals with browser components aside from the document,like history, location, navigator and screen (as well as some others that vary by browser). The Browser Object Model (BOM) in JavaScript includes the properties and methods for JavaScript to interact with the web browser. BOM provides you with window object, for example, to show the width and height of the window. It also includes the window.scre...
Post a Comment
Read more