Why is the subscribe method being executed after the return statement?

Currently, I have a form where new members can be added. Upon submitting the form, it is crucial to ensure that the email entered for the new user is not already in use. If the email is already associated with an existing member, an alert will pop up displaying the message: "Email is already in use!". On the other hand, if the email is unique, the user will be redirected to another view and an alert-success will be shown. The challenge I am facing is that when calling the service method to check if a new member has been created, the function returns the member undefined before it is properly filled in the subscription. Does anyone have any ideas on how to manage this situation and ensure that the subscribe is executed before the return?

Service Method:

    postMemberContactInfo(memberContactInfo: MemberContact){
          this._http
          .post<MemberContact>(this._membersUrl, memberContactInfo, {
            headers: new HttpHeaders({ 'Content-Type': 'application/json' }),
            responseType: 'json',
            observe: 'body',
          })
          .subscribe({
            next: (value) => { this._newMember = value },
            complete: () => { this.router.navigate([`/members/${this._newMember.id}`], {
              state: this._newMember
            } ) },
            error: (error) => catchError(this.handleError)
          })
    
        return this._newMember;
      }

Component TypeScript:

  onSubmit() {
    if (this.addMemberForm.invalid) this.addMemberForm.markAllAsTouched();
    else {
      let postedMember = this.memberAddService.postMemberContactInfo({
        name: this.getOrElse("name", ""),
        surname: this.getOrElse("surname", ""),
        role: this.getOrElse("role", ""),
        email: this.getOrElse("email", ""),
        username: this.getOrElse("username", ""),
        comments: this.getOrElse("comments", ""),
      });

      if (postedMember == undefined) this.showAlert = true;
      else {
        this.showAlert = false;
        this.newMemberCreated.emit(postedMember);
      }
    }
  }

Template:

     <app-generic-alert
      [ngClass]="showAlert ? 'd-block' : 'd-none'"
      [alertType]="'alert-danger'"
      [mainMessage]="'ERROR: '"
      [secondaryMessage]="'Email is already in use!'"
      (closeAlertEvent)="closeAlertHandler()"
    ></app-generic-alert>

Answer №1

Your Observable operates asynchronously, while your function runs synchronously.

This is the scenario in your code:

  1. When you invoke postMemberContactInfo, it immediately returns the current value of this._newMember
  2. Later (perhaps a few seconds after), when the backend server responds to the request made by
    this._http.post<MemberContact>
    , the subscription function is triggered asynchronously from the observable.

You should embrace the asynchronous nature of observables instead of attempting to force synchronous behavior... Check out this tutorial to help you get started

You can modify your service to return the observable:

postMemberContactInfo(memberContactInfo: MemberContact){
    return this._http
      .post<MemberContact>(this._membersUrl, memberContactInfo, {
        headers: new HttpHeaders({ 'Content-Type': 'application/json' }),
        responseType: 'json',
        observe: 'body',
      }).pipe(
        catchError((error) => this.handleError)
      );
  }

and then subscribe from the Component (something like the following example should work):


onSubmit() {
    if (this.addMemberForm.invalid) this.addMemberForm.markAllAsTouched();
    else {
      this.memberAddService.postMemberContactInfo({
        name: this.getOrElse("name", ""),
        surname: this.getOrElse("surname", ""),
        role: this.getOrElse("role", ""),
        email: this.getOrElse("email", ""),
        username: this.getOrElse("username", ""),
        comments: this.getOrElse("comments", ""),
      }).subscribe(newMember => {

        if (postedMember == undefined) this.showAlert = true;
        else {
          this.showAlert = false;
          this.newMemberCreated.emit(postedMember);

            this.router.navigate([`/members/${newMember.id}`], {
              state: newMember
            } )
        }
      });

      
    }
  }

Just a quick note, Subscribing directly from the component is usually considered an anti-pattern due to potential memory leaks. However, this method should be sufficient for now. Once you are comfortable with subscriptions, try to avoid direct subscribing and utilize the async pipe from your views instead.

Similar questions

If you have not found the answer to your question or you are interested in this topic, then look at other similar questions below or use the search

Ways to selectively apply colors to particular rows within an AntD table

I'm attempting to apply different colors to entire rows depending on certain data values from the table's data source. I know that we can utilize rowClassName, but I'm not entirely clear on its functionality. If anyone could provide exampl ...

Is there a sophisticated method for breaking down a nested property or member from TypeScript imports?

Just curious if it's possible, not a big deal otherwise. import * as yargs from 'yargs'; // default import I'm looking to extract the port or argv property. This would simplify the code from: bootstrap(yargs.argv.port || 3000) to: ...

What is the best way to implement a cascading menu with Angular material elements?

Looking to create a navigation menu that opens another menu alongside it. I've successfully set up a material nav list with a menu, but I'm struggling to position the second menu to the right of the initial navigation list as per my design. I tr ...

How to Pass a JSON Object to a Child Component in Angular and Display It Without Showing "[Object

Need help with my API call implementation. Here's a snippet from my Input component: Input.html <form (submit)="getTransactions()"> <div class="form-group"> <label for="exampleInputEmail1"></label> <input type="t ...

react-router: The 'history' type is not found in the current context

Here is some code snippet from App.tsx: interface AppProps{ history: any } export default class App extends React.Component<AppProps,...> { public state = { target: this.props.history.push('/') }; private route() { if (! ...

What is the best way to retrieve the `any` type when utilizing the `keyof` keyword?

I am struggling to articulate this question properly, so please refer to the code below interface TestParams<T> { order?: keyof T attr1?: number attr2?: string } async function Test<T = any>(_obj: TestParams<T>): Promise<T> { ...

Adding flair to a object's value in React JS

In my React JS file, I have a map function that I am using to populate a select dropdown with options. const options = response.map(k => ({ value: k.id, label: k.description ? `${k.name} - ${k.description}` : k.name, })); I ...

What are the steps to add code into the Monaco Editor using Playwright?

As I explore the world of Playwright, I am faced with a challenge regarding testing a feature that involves a monaco editor. Unfortunately, my search in Playwright documentation and forums did not yield any relevant information. Here is the test scenario ...

Exploring the Angular lifecycle hooks for directives: AfterContent and AfterView

According to the Angular documentation, it is stated that AfterContent and AfterView lifecycle hooks are intended for components and not directives. Surprisingly, I have a directive that seems to be using them without any issues. What potential limitation ...

Having an issue where the Material Angular 6 DatePicker is consistently displaying my selected date as one day earlier

I've encountered a strange issue with the current version of the Material Angular DatePicker. After upgrading from A5 to A6, it started to parse my date one day earlier than expected. You can see an example of this problem here: https://stackblitz.com ...

When using next.js, typescript, and jest together, an error may occur with the message "Unexpected token '

When attempting to run jest in my Typescript Next.js project, I encounter the following error: Details: node_modules/d3-scale/src/index.js:1 ({"Object.<anonymous>":function(module,exports,require,__dirname,__filename,jest){expo ...

Broaden the TypeScript interface with indexed types

Imagine a straightforward indexed interface: interface FormData { [K: string]: string; } This little fella works like a charm. However, there comes a time when I want to allow a property to be an array of strings. interface AcmeFormData extends Form ...

Effective ways to fill a Map<string, string> with input data

Check out this Stackblitz Here is the model I am working with: export class Items { items: Map<string, string>; createdBy: string; deliveredBy: string; } I am trying to dynamically generate input fields based on items in an array, but struggl ...

Prevent the array from altering its values

I am utilizing a mock-service that is configured in the following way: import { Article } from "./article"; export const ARTICLES: Article[] = [ new Article( 1, 'used', 5060639120949, 'Monster Energy& ...

The error was caused by my use of ng-template instead of the traditional template tag

I am currently working on an Angular 2 rc.1 application and facing an issue with overriding the existing pager by nesting a ng-template with the directive kendoPagerTemplate inside the kendo-grid. Here is an example of what I am trying to achieve: <ke ...

Altering a public variable of a component from a sibling component

Within my application, I have two sibling components that are being set from the app.component: <my-a></my-a> <my-b></my-b> The visibility of <my-a> is determined by a public variable in its component: @Component({ module ...

Issues arise when trying to type ChangeEvent in React using Typescript

After spending some time learning React with TypeScript, I encountered a problem. The prop onChangeHandler in my code takes a function to modify properties in formik values. <Formik<FormModel> initialValues={{ favorite: ...

Angular 2: Navigate without displaying information in the URL bar

Is there a method in Angular 2 to navigate and transmit data that is not visible in the URL? I am interested in developing a component that accepts a complicated object without revealing it in the URL. Appreciate any insights on this matter! ...

Is there an issue with validation when using looped radio buttons with default values in data-driven forms?

Within my reactive form, I am iterating over some data and attempting to pre-set default values for radio buttons. While the default values are being successfully set, the validation is not functioning as expected. <fieldset *ngIf="question.radioB ...

Creating a hybrid application with a mix of Angular and AngularJS - strategies for incorporating Angular modules into an AngularJS application

Looking to incorporate Angular components into an existing angularjs project that was created using gulp? Want to utilize downgradeModule to create a hybrid Angular/AngularJS app? Facing an issue with importing AppModule from the Angular project, as it is ...