Communication between Sibling components in Angular

Communication or data exchange between component is pretty common scenario in angular development. We know the property binding and event binding can be implemented for hierarchical communication, i.e to pass data from parent to child component and vice versa. We can implement common service scenario when there is need to communicate among sibling components.

Now, the question is can we implement same solution for parent child communication? The answer is yes, we can because service in angular is singleton in nature. So, it is single source of truth.

Now, let’s implement common service scenario as example.

Step 1) Create multiple component and subscribe common service in target component

Here is example code for that. We will create “SharedService” shortly. Here is code for “Work1” component.

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

import { SharedService } from '../services/SharedService'

@Component({

  selector: 'work1',

  template: `

  <input type="text" name="txtName" [(ngModel)]="name">

  <input type="button" name="Click" value="Click" (click)="refresh()">`

})

export class Work1 {

  name : string;

  constructor(private _sharedService: SharedService ){

  }

  refresh(){

    this._sharedService.publishData(this.name);

  }

}

Here the idea is, when user will click refresh, it will call one function in shared service. The function is responsible to push the data in an observable stream. As soon as service will push the data to stream, the subscriber of the stream will get notification.

Let’s create another component called “Work2”

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

import { SharedService } from '../services/SharedService'

@Component({

  selector: 'work2',

  template: `{{name}}`

})

export class Work2 {

  name : string;

  constructor(private _sharedService : SharedService){

    this._sharedService.name$.subscribe(

      data => {

          this.name = data;

      });

  }

}

Here, you can see that we are subscribing “name” observable in SharedService.  So, when there will be any change of “name” variable then the code within constructor should trigger.

Step2) Create common service.

Now, we will implement the common service which will function as mediator/event publisher in implementation.

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

import { Subject }    from 'rxjs/Subject';

@Injectable()

export class SharedService {

  private name = new Subject<string>(); 

  name$ = this.name.asObservable();

  publishData(data: string) {

    this.name.next(data);

  }

}

The pushData() function is responsible to push the current data to “name$” observable stream.

So, here is final output 

Evolution of AJAX World

If you have started you carrier around 7-10 years back as web developer then probably you have experienced the evaluation practically.

Because of huge advantage of AJAX, more or less 70-80 % of modern web application has adapted this technology. The new style of AJAX implementation came in market so quickly that it’s sometime hard to remember what things were before that?

Anyway, Long ago, Netscape added a feature in browser called live script which was capable to give flavor of offline processing like form validation in client side and bit more. Slowly Live script became JavaScript with more functionality and flexibility.

The inception of DynamicHTML has started in development world, slowly XML gain its popularity in AJAX world when Microsoft added a small function in IE5 to perform XMLHttpRequest call to server.

The classic AJAX using XMLHttpRequest

This is classic style to make AJAX call using vanilla JavaScript. If you worked in very old ASP, JSP or PHP application, probably you are familiar with this style of AJAX call.

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
       // Typical action to be performed when the document is ready:
       document.getElementById("demo").innerHTML = xhttp.responseText;
    }
};
xhttp.open("GET", "yourfilename.extension", true);
xhttp.send();

Oh, did I miss something? Yes, we need to detect browser prior to AJAX call, Just to make sure we are using proper XMLHttpRequest object. Yes, XMLHttpRequest object is browser specific.

JQuery changed the whole game

Then JQuery came in market, it played major role to change face of client side app development.  It combine and packed the above code into few lines and introduce the concept of Callback.

$.ajax({url: "yoururl.com", success: function(result){
        //enjoy with result variable

    }});

And that’s all, simple, compact, no code smell and maintainable. Now, in mean time other library too started wrapping classic XMLHttpRequest request using very similar syntax.

So, as a result the concept of callback has introduced in development world. The moto of callback is, call me once you have prepared the result, or call error in mess!.

Let’s return promise rather than actual result

People started to realize that, as it is asynchronous call, it should return something by which we can take decision. Let’s give some example. The below code is based on promise and then callback function.

requestSomeData("http://example.com ") // returns a promise for the response

    .then(function(response){ // ‘then’ is used to provide a promise handler

    

    return JSON.parse(response.body); // parse the body

    

   }) // returns a promise for the parsed body

    .then(function(data){

   

    return data.something; // get the price

   }) // returns a promise for the price

    .then(function(price){ // print out the price when it is fulfilled

        //do something with the data

  });

We can consider this as fully asynchronous execution plan, even if my JSON.parse() take huge time, the execution flow will not hang the thread because I have attached then callback to ensure that someone will take care once parse completed.

Angular and Other library utilize it best

Angular 1.X introduced a way to sync all asyn call using “$q” service. This is huge power to developer to process more than one asynchronous call and print consolidated result.

Want to have more control on AJAX call? Use Observable.

RxJs introduced the concept called Observable to have more grip on AJAX call. Let’s think that we need to cancel an AJAX call in middle. Assume, the situation where need to handle multiple AJAX call. Observable is preferred than promise here.

So, an observable is like a stream and allow to pass zero or more events where the callback is called for each event. The Observable covers more including promise.

For more info, please check Observable in Angular2

    

Learning Angular2 ? Here you map yourself !

What is new in angular2?

               Let's see, do I really need to learn!

Advantages of angular2

               If there, industry will adapt quickly and I have to spend some amount of time to learn. Good advantages are bad news for "coder by incident" Engineer :)

Does typescript really need in angular2?

               It could be gossip, let's check reality. Oh!! People are recommending to use typescript, so I have to learn it.

Setting up typescript environment and start Hello World (before that bit struggle with NPM)

               All YouTube tutorial are using Visual Studio Code, but I want to setup in my Visual Studio Enterprise edition :)

Let’s setup angular2 in Visual Studio

               Spent good amount of time in old angular2 website of Google. Setting up typings.js, common.js, tsconfig.js etc finally with webpack, no idea! What is happening! Confused!!

Try angular2 cli or inbuilt project template with ASP.NET Core 1.0

               Feel that ASP.NET Core 1.0 template is best solution, almost 0 setup and production ready architecture :)

Learn architecture of angular2

               Let’s hands on by writing baby component and understand architecture. Learn data binding, routing, Template, directory bla bla...

Dependency injection in angular2

               Oh.. Not much change with angular 1.X, easy to pick up if u know 1.x

Now, let's implement in memory CRUD/TODO app. And here I am...

Work with service in Angular2

Conceptually service is independent snippet of code which contains certain functionality or business logic. In Angular2 service is nothing but class of typescript (If we use typescript) which we can inject to component or module.

Yes, we can inject service to both component and module level. In this example we will demonstrate same.

If you are new in Angular2 , I will recommend to go through my previous article to setup angular2 project in IDE.

Setup Angular2 in Visual Studio

So, let’s start to implement one simple service which will return list of Person Object.

Add app.dataService.ts file in app folder. Here is content of file.

import {Injectable} from "@angular/core";

export interface Person {

    name: string

}

@Injectable()

export class dataService{

   

    getPerson(): Person[]

    {

        return [

            { name: "Ram" },

            { name: "Syam" },

            { name: "Jodu" }

        ];

    }

}

Here Person interface is type which we are returning from getPerson() function. Please note that the @Injectable decorator is needed when we want to inject to some other unit of code.

Inject service to component

As we said, service can be injectable both to component and module. Here we will inject service to component. Here we have created PersonComponent where we are injecting service in provider section.

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

import {dataService ,Person } from './app.dataservice'

import {OnInit} from "@angular/core";

@Component({

    selector: 'person',

    template: `<ul>

    <li *ngFor="let p of _persons">{{p.name}}</li>

    </ul>`,

    providers: [dataService],

})

export class PersonComponent {

    public _persons: Person[];

    constructor(private _dataService: dataService)

    {

        this._persons = this._dataService.getPerson();

    }

}

In constructor we are consuming getPerson() function which populating _Person member. Now, let’s create a view to display the component. Here is our sample view.

<!DOCTYPE html>

<html>

<head lang="en">

    <base href="/">

    <meta charset="UTF-8">

    <meta name="viewport" content="width=device-width, initial-scale=1">

    <!-- Polyfill(s) for older browsers -->

    <script src="node_modules/core-js/client/shim.min.js"></script>

   

    <script src="node_modules/zone.js/dist/zone.js"></script>

    <script src="node_modules/reflect-metadata/Reflect.js"></script>

    <script src="node_modules/systemjs/dist/system.src.js"></script>

    <!-- Configure SystemJS -->

    <script src="systemjs.config.js"></script>

   

    <script>

      System.import('app').catch(function(err){ console.error(err); });

    </script>

</head>

<body>

    <person>Loading App...</person>

</body>

</html>

Once we run the application ,we will see that data is showing like this.

Inject service in module

Now, let’s see how we can inject service to module. Here mainModule of application where we are injecting service in provider section.

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

import { BrowserModule } from '@angular/platform-browser';

import { PersonComponent } from './app.main_component';

import { dataService} from './app.dataservice';

@NgModule({

    imports: [BrowserModule ],

    declarations: [PersonComponent],

    bootstrap: [PersonComponent],

    providers: [dataService]

})

export class mainModule

{

};

Now, we can use the service in PersonComponent without inject it.

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

import {dataService, Person } from './app.dataservice'

import {OnInit} from "@angular/core";

@Component({

    selector: 'person',

    template: `<ul>

    <li *ngFor="let p of _persons">{{p.name}}</li>

    </ul>`

})

export class PersonComponent {

    public _persons: Person[];

    constructor(private _dataService: dataService) {

        this._persons = this._dataService.getPerson();

        console.log(JSON.stringify(this._persons));

    }

}