Mastering the Use of Interfaces in Ionic/Angular

My journey into angular/ionic app development is just beginning. I came across the following piece of advice recently

Interfaces are only at compile time. This allows only you to check that the expected data received follows a particular structure.

Currently, I am working on an ionic app where the API services return data to the user. Let's consider a login function scenario where the API service returns data upon login request.

In my Ionic project, I have created a provider through which HTTP calls are made to the API using HTTPClient.

//Provider

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';

interface LoginResponse {
  success: boolean;
  message: string;
  token: string;
  userId: number;
}
@Injectable()
export class LoginServicesProvider {
  constructor(public http: HttpClient) {
  }

  login(reqData): Observable<LoginResponse[]> {
    return this.http.post<LoginResponse[]>('localhost:3000/api/login', reqData);
  }
}

By examining the code above, it is evident that I've defined an interface named LoginResponse

Below is the code snippet for the Login component:

//Component

import { LoginServicesProvider } from './../../providers/login-services/login-services';
import { Component } from '@angular/core';
import { Observable } from 'rxjs/Observable';

@Component({
  selector: 'page-login-page',
  templateUrl: 'login-page.html',
})
export class LoginPage {
  constructor(private loginService: LoginServicesProvider) {
  }

  onSubmit() {
    let reqParams = {
    email: '<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="d6b7b0b7bdb3b3bbb7bfba96bfb2f8b5b9bb">[email protected]</a>',
    password: 'password',
    };

    this.loginService.login(reqParams).subscribe(res => {
        console.log('success');
    });
  }
}

For now, the example merely logs a message to the console.

Now, here are my queries

1) In accordance with the earlier statement, does my LoginResponse interface effectively validate the incoming data? If not, how and where should I implement such validation- in the provider or the component?

2) Assuming I have multiple interfaces within a single provider, one for login data and another for user profile data, among others, where should I organize them? Can I segregate them into separate files and export them? I haven't come across any specific ionic commands to create interfaces

Thank you! I'm determined to kickstart my career on the right foot and avoid common pitfalls. That's why I decided to seek guidance through this post.

Answer №1

Interfaces in Typescript serve as a blueprint for the structure of an object. When an object is created in TypeScript, the compiler can determine if it fits the interface criteria. However, at runtime, interfaces are removed, thus no validation is done to check compatibility with interfaces. Utilizing post<T> indicates to the compiler the expected shape of the response object as T, but no verification is carried out.

You have the flexibility to include numerous interfaces within a file and export them for use in other files similar to classes or functions. The organization of your code is entirely up to you.

If you wish to ensure proper implementation of an object at runtime, refer to this resource

Answer №2

Interfaces in TypeScript serve to define a contract, as mentioned. In the example provided, the interface outlines the expected properties of a login response from the server. It's important to note that interfaces do not require all properties returned in the JSON response to be explicitly mentioned. Additional properties can be included in the interface if needed.

To implement this concept, a new file named ILoginRequest.ts is created with an interface called ILoginRequest:

export interface ILoginRequest {
 email:string;
 password:string;
}

This interface is then used as the type for the requestData input parameter in the provider class:

login(reqData:ILoginRequest ): Observable<LoginResponse[]> {
return this.http.post<LoginResponse[]>('localhost:3000/api/login', reqData);

This approach helps clarify the expected API specifications when reviewing code in the future. By utilizing interfaces, it becomes clear what inputs are required and what outputs can be expected from specific functions.

In the calling page, the output from the API is assigned to the loginResponse variable, which is of type LoginResponse interface. This provides clarity on the available properties and enables IDEs to provide IntelliSense support:

export class LoginPage {
 private loginResponse : LoginResponse;
 constructor(private loginService: LoginServicesProvider) {
 }

onSubmit() {
let reqParams = {
email: 'example@email.com',
password: 'password',
};

this.loginService.login(reqParams).subscribe((res:LoginResponse) => {
    console.log('success');
    this.loginResponse = res;
});

} }

For further information on using interfaces in TypeScript, refer to this link.

Regarding where to store interfaces, it is ultimately up to individual developer preference. A common practice is to create a separate 'interfaces' folder within the 'app' directory and create new files for each interface.

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