Lesson 14 - Add HTTP communication to your app

This tutorial demonstrates how to integrate HTTP and an API into your app.

Up until this point your app has read data from a static array in an Angular service. The next step is to use a JSON server that your app will communicate with over HTTP. The HTTP request will simulate the experience of working with data from a server.

Time required: expect to spend about 20 minutes to complete this lesson.

Before you start

This lesson starts with the code from the previous lesson, so you can:

• Use the code that you created in Lesson 13 in your integrated development environment (IDE).
• Start with the code example from the previous lesson. Choose the from Lesson 13 where you can:
  • Use the live example in StackBlitz, where the StackBlitz interface is your IDE.
  • Use the download example and open it in your IDE.

If you haven't reviewed the introduction, visit the Introduction to Angular tutorial to make sure you have everything you need to complete this lesson.

After you finish

• Your app will use data from a JSON server

Lesson steps

Perform these steps in the terminal on your local computer.

Step 1 - Configure the JSON server

JSON Server is an open source tool used to create mock REST APIs. You'll use it to serve the housing location data that is currently stored in the housing service.

1. Install json-server from npm by using the following command.

   npm install -g json-server

2. In the root directory of your project, create a file called db.json. This is where you will store the data for the json-server.

3. Open db.json and copy the following code into the file

   {
   "locations": [
   {
   "id": 0,
   "name": "Acme Fresh Start Housing",
   "city": "Chicago",
   "state": "IL",
   "photo": "/assets/bernard-hermant-CLKGGwIBTaY-unsplash.jpg",
   "availableUnits": 4,
   "wifi": true,
   "laundry": true
   },
   {
   "id": 1,
   "name": "A113 Transitional Housing",
   "city": "Santa Monica",
   "state": "CA",
   "photo": "/assets/brandon-griggs-wR11KBaB86U-unsplash.jpg",
   "availableUnits": 0,
   "wifi": false,
   "laundry": true
   },
   {
   "id": 2,
   "name": "Warm Beds Housing Support",
   "city": "Juneau",
   "state": "AK",
   "photo": "/assets/i-do-nothing-but-love-lAyXdl1-Wmc-unsplash.jpg",
   "availableUnits": 1,
   "wifi": false,
   "laundry": false
   },
   {
   "id": 3,
   "name": "Homesteady Housing",
   "city": "Chicago",
   "state": "IL",
   "photo": "/assets/ian-macdonald-W8z6aiwfi1E-unsplash.jpg",
   "availableUnits": 1,
   "wifi": true,
   "laundry": false
   },
   {
   "id": 4,
   "name": "Happy Homes Group",
   "city": "Gary",
   "state": "IN",
   "photo": "/assets/krzysztof-hepner-978RAXoXnH4-unsplash.jpg",
   "availableUnits": 1,
   "wifi": true,
   "laundry": false
   },
   {
   "id": 5,
   "name": "Hopeful Apartment Group",
   "city": "Oakland",
   "state": "CA",
   "photo": "/assets/r-architecture-JvQ0Q5IkeMM-unsplash.jpg",
   "availableUnits": 2,
   "wifi": true,
   "laundry": true
   },
   {
   "id": 6,
   "name": "Seriously Safe Towns",
   "city": "Oakland",
   "state": "CA",
   "photo": "/assets/phil-hearing-IYfp2Ixe9nM-unsplash.jpg",
   "availableUnits": 5,
   "wifi": true,
   "laundry": true
   },
   {
   "id": 7,
   "name": "Hopeful Housing Solutions",
   "city": "Oakland",
   "state": "CA",
   "photo": "/assets/r-architecture-GGupkreKwxA-unsplash.jpg",
   "availableUnits": 2,
   "wifi": true,
   "laundry": true
   },
   {
   "id": 8,
   "name": "Seriously Safe Towns",
   "city": "Oakland",
   "state": "CA",
   "photo": "/assets/saru-robert-9rP3mxf8qWI-unsplash.jpg",
   "availableUnits": 10,
   "wifi": false,
   "laundry": false
   },
   {
   "id": 9,
   "name": "Capital Safe Towns",
   "city": "Portland",
   "state": "OR",
   "photo": "/assets/webaliser-_TPTXZd9mOo-unsplash.jpg",
   "availableUnits": 6,
   "wifi": true,
   "laundry": true
   }
   ]
   }

4. Save this file.

5. Time to test your configuration. From the command line, at the root of your project run the following commands.

   json-server --watch db.json

6. In your web browser, navigate to the http://localhost:3000/locations and confirm that the response includes the data stored in db.json.

If you have any trouble with your configuration, you can find more details in the official documentation.

Step 2 - Update service to use web server instead of local array

The data source has been configured, the next step is to update your web app to connect to it use the data.

1. In src/app/housing.service.ts, make the following changes:

   1. Update the code to remove housingLocationList property and the array containing the data.

   2. Add a string property called and set the value to 'http://localhost:3000/locations'

      url = 'http://localhost:3000/locations';

      This code will result in errors in the rest of the file because it depends on the housingLocationList property. We're going to update the service methods next.

   3. Update the getAllHousingLocations function to make a call to the web server you configured.

      async getAllHousingLocations(): Promise<HousingLocation[]> {
        const data = await fetch(this.url);
        return await data.json() ?? [];
      }

      The code now uses asynchronous code to make a get request over HTTP. Notice, for this example, the code uses fetch. For more advanced use cases consider using HttpClient provided by Angular.

   4. Update the getHousingLocationsById function to make a call to the web server you configured.

      async getHousingLocationById(id: number): Promise<HousingLocation | undefined> {
        const data = await fetch(`${this.url}/${id}`);
        return await data.json() ?? {};
      }

   5. Once all the updates are complete, your updated service will match the following code.

      import { Injectable } from '@angular/core';
      import { HousingLocation } from './housinglocation';
      
      @Injectable({
        providedIn: 'root'
      })
      export class HousingService {
      
        url = 'http://localhost:3000/locations';
      
        async getAllHousingLocations(): Promise<HousingLocation[]> {
          const data = await fetch(this.url);
          return await data.json() ?? [];
        }
      
        async getHousingLocationById(id: number): Promise<HousingLocation | undefined> {
          const data = await fetch(`${this.url}/${id}`);
          return await data.json() ?? {};
        }
      
        submitApplication(firstName: string, lastName: string, email: string) {
          console.log(firstName, lastName, email);
        }
      }

Step 3 - Update the components to use asynchronous calls to the housing service

The server is now reading data from the HTTP request but the components that rely on the service now have errors because they were programmed to use the synchronous version of the service.

1. In src/app/home/home.component.ts, update the constructor to use the new asynchronous version of the getAllHousingLocations method.

   constructor() {
     this.housingService.getAllHousingLocations().then((housingLocationList: HousingLocation[]) => {
       this.housingLocationList = housingLocationList;
       this.filteredLocationList = housingLocationList;
     });
   }

2. In src/app/details/details.component.ts, update the constructor to use the new asynchronous version of the getHousingLocationById method.

   constructor() {
     const housingLocationId = parseInt(this.route.snapshot.params['id'], 10);
     this.housingService.getHousingLocationById(housingLocationId).then(housingLocation => {
       this.housingLocation = housingLocation;
     });
   }

3. Save your code.

4. Open the application in the browser and confirm that it runs without any errors.

Lesson review

In this lesson, you updated your app to:

• use a local web server (json-server)
• use asynchronous service methods to retrieve data.

Congratulations! You've successfully completed this tutorial and are ready to continue your journey with building even more complex Angular Apps. If you would like to learn more, please consider completing some of Angular's other developer tutorials and guides.