Angular wait for subscribe to finish

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Query: How to make Angular wait for a subscribe to finish?

Answer: In Angular, you can use the `flatMap` operator to chain observables and make sure certain code only executes after an observable has completed. Here’s an example:

    
      import { Component, OnInit } from '@angular/core';
      import { HttpClient } from '@angular/common/http';
      import { concatMap } from 'rxjs/operators';

      @Component({
        selector: 'app-example',
        template: `
          
          
{{ data }}

        `
      })
      export class ExampleComponent implements OnInit {
        data: any;

        constructor(private http: HttpClient) { }

        ngOnInit() {
        }

        getData() {
          this.http.get('https://jsonplaceholder.typicode.com/posts/1').pipe(
            concatMap(response => {
              this.data = response;
              return this.http.get('https://jsonplaceholder.typicode.com/comments?postId=1');
            })
          ).subscribe(comments => {
            console.log(comments);
            // Do something with the comments data
          });
        }
      }

In this example, when the “Load Data” button is clicked, the `getData()` method is called. Inside this method, we make an HTTP GET request to retrieve a post from a mock API endpoint. We use the `concatMap` operator to chain this observable and assign the response to the `data` property.

Then, we chain another observable by making another HTTP GET request to retrieve comments related to the retrieved post. Finally, we subscribe to this chained observable and handle the comments data. The `console.log()` statement is just an example to show that you can perform any actions with the response data inside the `subscribe()` callback.

This setup ensures that the second HTTP request is only made after the first one has completed successfully. This way, Angular waits for the first subscribe to finish before executing the subsequent code.

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In this example, I have encapsulated the provided query along with a detailed answer in a `

` tag. The answer explains the use of the `flatMap` operator in Angular and provides a code example to demonstrate its usage.

Please note that the example code assumes the presence of the necessary Angular and RxJS imports, as well as the usage of the `HttpClient` module for making HTTP requests. You may need to adjust the code to fit your specific project setup.

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