Angular rxjs Distinctions

Question

Angular rxjs Distinctions

Coming from AngularJS to Angular, I'm still trying to wrap my head around rxjs observable.

For example:

User.ts

export class User {
id?:any;
username:string;
password:string;
}

Using <User[]>

myUser(header: any) {
const url = `${this.mainUrl}/my_user`;
return this.http.get<User[]>(url, header).pipe(
  map(resp => {
    return resp;
  })
);
}

Not using <User[]>

myUser(header: any) {
const url = `${this.mainUrl}/my_user`;
return this.http.get(url, header).pipe(
  map(resp => {
    return resp;
  })
);
}

Both methods seem to give the same result. So I'm unsure of the significance of including it or not.

UPDATE:

The data I'm fetching looks nothing like my User.ts file, but surprisingly no errors are being thrown.

{
"username": "mhqadmin",
"inserted_at": "2019-02-06T07:01:17.024874",
"id": "b491e7c3-da11-40fe-b4b7-8f97fa88a9fd",
"avatar": {
    "middlename": "mhqadmin",
    "lastname": "headquarters",
    "id": "939c2eec-573e-4245-adcc-0771c73f22e4",
    "firstname": "marte"
},
"app_role": "mhq-admin",
"app_permission": true
}

angular typescript

Answer 1

Answer №1

When using this.http.get<User[]> compared to this.http.get, the main distinction is that you are specifying a type within the generic signature of get.

According to the Angular source code:

  get<T>(url: string, options?: {
    headers?: HttpHeaders | {[header: string]: string | string[]},
    observe?: 'body',
    params?: HttpParams|{[param: string]: string | string[]},
    reportProgress?: boolean,
    responseType?: 'json',
    withCredentials?: boolean,
  }): Observable<T>;

The usage of get<T> represents a generic type signature, allowing you to define the expected data structure. By invoking this.http.get<User[]>, you are essentially indicating that the returned data should conform to an array of type User. However, this concept is rooted in TypeScript and doesn't directly impact RxJS/Observables or JavaScript functionalities. When calling this.http.get, the operation simply triggers an HTTP request for data without any predefined type specification.

In order to tailor the retrieved data to match your User.ts class structure, simply defining the type as this.http.get<User[]> won't alter the data itself; it merely serves as a guideline for the compiler. To manipulate the data format accordingly, you would need to extract and reformat the relevant fields, as demonstrated below:

myUser(header: any) {
  const url = `${this.mainUrl}/my_user`;
  return this.http.get(url, header).pipe(
    map(resp => {
      return {
        id: resp.id,
        username: resp.username
      };
    })
  );
}

This snippet showcases aligning the data output with an interface/class like the following:

interface User {
  id: string;
  username: string;
}

However, keep in mind that the actual data structure being received likely adheres more closely to a model such as:

interface User {
  username: string;
  inserted_at: string;
  id: string;
  avatar: Avatar;
  app_role: Role;
  app_permission: boolean;
}

If you specify a type within the generic parameter, that defines the expected output model from the Observable. To accurately map this output to the correct interface, adjustments must be made as illustrated in the map example.

Answer 2

When using this.http.get<User[]> compared to this.http.get, the main distinction is that you are specifying a type within the generic signature of get.

According to the Angular source code:

  get<T>(url: string, options?: {
    headers?: HttpHeaders | {[header: string]: string | string[]},
    observe?: 'body',
    params?: HttpParams|{[param: string]: string | string[]},
    reportProgress?: boolean,
    responseType?: 'json',
    withCredentials?: boolean,
  }): Observable<T>;

The usage of get<T> represents a generic type signature, allowing you to define the expected data structure. By invoking this.http.get<User[]>, you are essentially indicating that the returned data should conform to an array of type User. However, this concept is rooted in TypeScript and doesn't directly impact RxJS/Observables or JavaScript functionalities. When calling this.http.get, the operation simply triggers an HTTP request for data without any predefined type specification.

In order to tailor the retrieved data to match your User.ts class structure, simply defining the type as this.http.get<User[]> won't alter the data itself; it merely serves as a guideline for the compiler. To manipulate the data format accordingly, you would need to extract and reformat the relevant fields, as demonstrated below:

myUser(header: any) {
  const url = `${this.mainUrl}/my_user`;
  return this.http.get(url, header).pipe(
    map(resp => {
      return {
        id: resp.id,
        username: resp.username
      };
    })
  );
}

This snippet showcases aligning the data output with an interface/class like the following:

interface User {
  id: string;
  username: string;
}

However, keep in mind that the actual data structure being received likely adheres more closely to a model such as:

interface User {
  username: string;
  inserted_at: string;
  id: string;
  avatar: Avatar;
  app_role: Role;
  app_permission: boolean;
}

If you specify a type within the generic parameter, that defines the expected output model from the Observable. To accurately map this output to the correct interface, adjustments must be made as illustrated in the map example.

Answer 3

Answer №2

When you include <User[]> in your Typescript code, you are specifically telling Typescript that the result of http.get will be an Observable<User[]>. This allows Typescript to accurately infer the type of variable myUser as Observable<User[]>. This proves helpful later in your development process since it enables better tooling support by providing information on the properties available in your response types and catching any typos or mistakes during compilation. The use of generics in http.get allows you to define the expected response type (however, if not specified, it defaults to any).

If you omit <User[]>, Typescript will default to the any type, essentially offering no additional advantages over regular javascript.

Furthermore, the map(resp => { return resp; }) function is unnecessary and can be safely removed from your code.

Answer 4

When you include <User[]> in your Typescript code, you are specifically telling Typescript that the result of http.get will be an Observable<User[]>. This allows Typescript to accurately infer the type of variable myUser as Observable<User[]>. This proves helpful later in your development process since it enables better tooling support by providing information on the properties available in your response types and catching any typos or mistakes during compilation. The use of generics in http.get allows you to define the expected response type (however, if not specified, it defaults to any).

If you omit <User[]>, Typescript will default to the any type, essentially offering no additional advantages over regular javascript.

Furthermore, the map(resp => { return resp; }) function is unnecessary and can be safely removed from your code.

Angular rxjs Distinctions

Answer №1

Answer №2

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