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What are the differences between Angular 2 Observables & Promises?

What are the features of Angular 2 Service?
The Angular 2 is using services concept and it provide the multiple features to us that are,
1.      Services are singleton objects.
2.      Services are capable of returning the data in the form promises or observables.
3.      Service class is decorated with Injectable decorator.
4.      The Injectable decorator is required only if our service class is making use of some Angular injectable like Http, Response and HttpModule service within it.

What are the differences between Observables & Promises?
1.      Promise:- Promises are only called once and It can return only a single value at a time and the Promises are not cancellable.
2.      Observables:- Observables handle multiple values over time and it can return multiple values and the Observables are cancellable.
3.      The Observables are more advanced than Promises.

Example as,
I hope this will help you to understand and create the basic of Angular 2 service. I am creating a user service and this user service returns the list of users.

After creating user service, I will use the user service “getUsers()” method in the user component’s ngOnInit() method to load the returns user collections on user screen.

I am also using the REST API Url ( and this RESTful API will returns the users.

app.module.ts :-

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { UniversalModule } from 'angular2-universal';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { HttpModule } from '@angular/http';
import { AppComponent } from './components/app/app.component';
import { UserComponent } from './components/user/user.component';
import { HeaderComponent } from './components/shared/header/header.component';
import { MenuComponent } from './components/menu/menu.component';
import { LoginComponent } from './components/login/login.component';
import { RegistrationComponent } from './components/registration/registration.component';

    bootstrap: [ AppComponent ],
    declarations: [
    imports: [
        RouterModule.forRoot([ //RouterModule.forRoot method in the module imports to configure the router.
            { path: '', redirectTo: 'user', pathMatch: 'full' },
            { path: 'user/:id', component: UserComponent }, //HERE ID IS A ROUTE PARAMETER.
            { path: 'login', component: LoginComponent },
            { path: 'registration', component: RegistrationComponent },
            { path: '**', redirectTo: 'user' }
export class AppModule {

user.component.ts and user.service.ts :-

import { Component, Injectable} from '@angular/core';
import { CommonModule } from '@angular/common';
import { HttpModule, Http, Response } from '@angular/http';

export class UserService {
     constructor(private _http: Http) {  }

    getUsers(apiUrl) {
        return this._http.get(apiUrl).map((data: Response) => data.json());

    selector: 'user',
    templateUrl: './user.component.html',
    styleUrls: ['./user.component.css'],
    providers: [UserService]

export class UserComponent {
    users = [];

    userRestApiUrl: string = '';

    constructor(private userService: UserService) {  }

    ngOnInit() {
        this.userService.getUsers(this.userRestApiUrl).subscribe(data => this.users = data);

user.component.html :-

<div class="row">
<div class="col-lg-12">
    <div class="ibox float-e-margins">
        <div class="ibox-title">
            <h2>Angular 2 - User Services</h2>
        <hr />
        <div class="ibox-content">
            <div class="table-responsive">
                <table class="table table-striped">
                            <th>Name </th>
                            <th>Description </th>
                            <th>URls </th>
                        <tr *ngFor="let user of users; let i = index">
                            <td><a href="{{user.public_members_url}}"> {{user.public_members_url}}</a></td>                              

Result :-

Note – If you need the example source code, email me and will send you code.

I hope you are enjoying with this post! Please share with you friends. Thank you!!
By Anil Singh | Rating of this article (*****)

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