In the first part of the beginner's guide to Angular tutorial series, you learnt what components are in Angular 4 and how to write Angular components.
In this part of the tutorial series, you'll learn what services are in Angular and how to use them.
You'll start by cloning the source code from the first part of the tutorial series.
git clone https://github.com/royagasthyan/AngularComponent.git
Once you have the source code, navigate to the project directory and install the required dependencies.
cd AngularComponent npm install
After the dependencies have been installed, start the application by typing the following command:
ng serve
You should have the application running on http://localhost:4200/.
In an Angular application, components deal with presenting the data to the view. Fetching data for the components to display is handled by Angular services.
Since the data fetching portion is handled separately in Angular services, it makes it easier to mock test services.
From the official documentation:
Components shouldn't fetch or save data directly and they certainly shouldn't knowingly present fake data. They should focus on presenting data and delegate data access to a service.
In this tutorial, you'll see how to create an Angular service for fetching data for an Angular component.
Another advantage of using Angular services is that it makes it easier to share data between two separate components.
In this tutorial, you'll be creating a word component which would search the query word entered by the end user against an API and return the search result.
You'll be making the API call by using an Angular service. So let's get started by creating an Angular component.
Navigate to the project directory and create a folder called word
.
Inside the word
project directory, create a file called word.component.html
. Add the following HTML code:
<h2> Word Component </h2> <div> <input type="text"> </div>
Create a file called word.component.ts
which would control the word.component.html
template. Here is how it looks:
import { Component } from '@angular/core'; @Component({ selector: 'word', templateUrl: 'word.component.html', styleUrls: ['word.component.css'] }) export class WordComponent { constructor(){ } }
As seen in the above code, you just created the WordComponent
class which would control the word.component.html
template file.
It has a @component
decorator where you have defined the selector
using which it would be accessible, the templateUrl
, and the component styleUrls
.
Once you have created the component, you need to add the component class to the NgModule
.
Open the app.module.ts
file inside the src/app
directory and import the new WordComponent
.
import { WordComponent } from './word/word.component'
Include the WordComponent
inside the NgModule
declarations. Here is how the app.module.ts
file looks:
import { BrowserModule } from '@angular/platform-browser'; import { NgModule } from '@angular/core'; import { AppComponent } from './app.component'; import { CalcComponent } from './calc/calc.component' import { WordComponent } from './word/word.component' import { FormsModule } from '@angular/forms'; @NgModule({ declarations: [ AppComponent, CalcComponent, WordComponent ], imports: [ BrowserModule, FormsModule ], providers: [], bootstrap: [AppComponent] }) export class AppModule { }
Open the app.component.html
file inside the src/app
folder and add the new WordComponent
using the defined selector. Here is how it looks:
<div style="text-align:center"> <word></word> </div>
Save the above changes and restart the server. You should have the word component displayed when loading the application.
Let's create an Angular service to query the word against a service URL which would return synonyms of the word.
You'll be using the Datamuse API for querying a keyword.
Create a file called word.service.ts
inside the src/app/word
folder. You'll be using the @Injectable()
decorator to make the service class available for injection.
Here is how the word.service.ts
file would look:
import { Injectable } from '@angular/core'; @Injectable() export class WordService { constructor(){ } }
In order to make an API call, you'll be using the HTTP
module. Import the HttpModule
in the src/app/app.module.ts
file. Here is how the file looks:
import { BrowserModule } from '@angular/platform-browser'; import { NgModule } from '@angular/core'; import { AppComponent } from './app.component'; import { CalcComponent } from './calc/calc.component' import { WordComponent } from './word/word.component' import { FormsModule } from '@angular/forms'; import { HttpModule } from '@angular/http'; @NgModule({ declarations: [ AppComponent, CalcComponent, WordComponent ], imports: [ BrowserModule, FormsModule, HttpModule ], providers: [], bootstrap: [AppComponent] }) export class AppModule { }
Import the Http
module inside the word.service.ts
file to make API calls.
import { Http } from '@angular/http';
You'll be making API calls to the following URL.
https://api.datamuse.com/words?max=10&ml=
You need to append the query keyword along with the above URL to get a maximum of 10 synonyms of the query term.
Define the variable url
inside the WordService
class and initialize it inside the constructor method.
export class WordService { url: string constructor(private http : Http){ this.url = 'https://api.datamuse.com/words?max=10&ml=' } }
You have declared and initialized the http
variable, which you'll use while making API calls.
Define a method called search_word
which would return the result of the API call as JSON
. Here is how it looks:
search_word(term){ return this.http.get(this.url + term).map(res => { return res.json() }) }
As seen in the above code, you have made a GET
request to the API URL using the Angular Http
module and returned the response as JSON
. Here is how the word.service.ts
file looks:
import { Injectable } from '@angular/core'; import { Http } from '@angular/http'; import 'rxjs/add/operator/map' @Injectable() export class WordService { url: string constructor(private http : Http){ this.url = 'https://api.datamuse.com/words?max=10&ml=' } search_word(term){ return this.http.get(this.url + term).map(res => { return res.json() }) } }
Now that you have the word service ready to make the API calls, you need to define the WordService
as the provider in the WordComponent
.
Import the WordService
in the word.component.ts
file.
import { WordService } from './word.service';
Define the providers
in the Angular WordComponent
.
@Component({ selector: 'word', templateUrl: 'word.component.html', styleUrls: ['word.component.css'], providers : [WordService] })
Initialize the WordService
inside the constructor
method.
constructor(private service: WordService){ }
Define a method called search
inside the word.component.ts
file which would call the service method. Inside the search
method, subscribe to the search_word
method from the WordService
.
search(term){ this.service.search_word(term).subscribe(res => { this.words = res; }) }
Here is how the modified word.component.ts
file looks:
import { Component } from '@angular/core'; import { WordService } from './word.service'; @Component({ selector: 'word', templateUrl: 'word.component.html', styleUrls: ['word.component.css'], providers : [WordService] }) export class WordComponent { words : any; constructor(private service: WordService){ } search(term){ this.service.search_word(term).subscribe(res => { this.words = res; }) } }
Add the enter key press event to the input element in the word.component.html
file.
<input #query (keyup.enter)="search(query.value)" type="text">
After entering a query term when the user presses the enter key, it would make a call to the search method in the word.component.ts
file.
As seen in the search
method inside the word.component.ts
file, you are collecting the response inside the words
variable as a list. So let's iterate the words
list and display in the word.component.html
file.
Modify the word.component.html
file as shown:
<div> <ul> <li *ngFor="let item of words"> {{item.word}} </li> </ul> </div>
Save the above changes and restart the server. Enter a keyword and press the enter key, and you should have the result populated as a list.
In this tutorial, you learnt what Angular services are. You learnt how to create Angular services and use them from an Angular component. You created a Word component which queries the entered keyword against an Angular service and displays the returned data in the component template file.
How was your experience learning Angular services? Do let us know your thoughts and suggestions in the comment section below.
Source code from this tutorial is available on GitHub.
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