Accessing Angular's Observable Objects

Question

Accessing Angular's Observable Objects

I am currently in the process of learning Angular and trying to work with Observables. However, I am facing an issue where I cannot extract data from an Observable when it is in object form.

public rowData$!: Observable<any[]>;

UpdateGrid() {
  this.rowData$ = this.http
    .get<any[]>('http://localhost:8080/data');
    this.rowData$.forEach(value => console.log(value));
}

When I log the output to the console, I receive the following HTTP response:

(2) [{…}, {…}]
 0: {id: 1, name: 'Bob', sex: 'Male'}
 1: {id: 2, name: 'Susan', sex: 'Female'}
length: 2
[[Prototype]]: Array(0)

I have tried using mapping and other methods to extract the data, but each time I end up with [object Object] displayed in the HTML.

Is there a simple way to retrieve this data? Any assistance would be greatly appreciated as I have been unable to find a solution online or make sense of the examples provided in the documentation. Thank you.

angular typescript rxjs observable ag-grid

Answer 1

Answer №1

There are essentially two questions to address here. Firstly, how to display the array as a string within your template for debugging purposes. Secondly, how to modify the array before passing it to ag-grid. Let's tackle these one by one.

Displaying Observable data in the template

When binding HTML content using interpolation syntax ({{ }}), Angular automatically invokes the toString() method if the object is not primitive. By default, objects will return [object Object] unless overridden. For arrays, values are typically joined by commas and nested objects call toString(). This explains the current output you're seeing.

To handle this, either customize the inner objects' toString(), or use Angular's | json pipe which internally utilizes JSON.stringify().

For example with your data:

<!-- Displays "[object Object]" for Observables -->
{{ rowData$ }} 

<!-- Shows "[object Object],[object Object]" for an array of Objects -->
{{ rowData$ | async }}

<!-- 
Output:
[ {id: 1, name: 'Bob', sex: 'Male'}, {id: 2, name: 'Susan', sex: 'Female'} ] 
thanks to the json pipe
-->
{{ rowData$ | async | json }}

Data Transformation

As you haven't specified the desired format, I'll demonstrate where you can apply transformation logic using observables in general.

An observable's .pipe() function allows applying operators like the map operator. This is handy when transforming received values, such as converting the array into a new structure.

import { map } from 'rxjs/operators'; // <-- import necessary operator

@Component({ /* omitted */ })
export class MyComponent {
  public rowData$!: Observable<any[]>;

  updateGrid() {
    this.rowData$ = this.http
      .get<any[]>('http://localhost:8080/data')
      .pipe(
        map(rowData => 
          rowData.map(entry => {
            // transform each object as needed
          }); 
        ) 
      );
  }
}

Answer 2

There are essentially two questions to address here. Firstly, how to display the array as a string within your template for debugging purposes. Secondly, how to modify the array before passing it to ag-grid. Let's tackle these one by one.

Displaying Observable data in the template

When binding HTML content using interpolation syntax ({{ }}), Angular automatically invokes the toString() method if the object is not primitive. By default, objects will return [object Object] unless overridden. For arrays, values are typically joined by commas and nested objects call toString(). This explains the current output you're seeing.

To handle this, either customize the inner objects' toString(), or use Angular's | json pipe which internally utilizes JSON.stringify().

For example with your data:

<!-- Displays "[object Object]" for Observables -->
{{ rowData$ }} 

<!-- Shows "[object Object],[object Object]" for an array of Objects -->
{{ rowData$ | async }}

<!-- 
Output:
[ {id: 1, name: 'Bob', sex: 'Male'}, {id: 2, name: 'Susan', sex: 'Female'} ] 
thanks to the json pipe
-->
{{ rowData$ | async | json }}

Data Transformation

As you haven't specified the desired format, I'll demonstrate where you can apply transformation logic using observables in general.

An observable's .pipe() function allows applying operators like the map operator. This is handy when transforming received values, such as converting the array into a new structure.

import { map } from 'rxjs/operators'; // <-- import necessary operator

@Component({ /* omitted */ })
export class MyComponent {
  public rowData$!: Observable<any[]>;

  updateGrid() {
    this.rowData$ = this.http
      .get<any[]>('http://localhost:8080/data')
      .pipe(
        map(rowData => 
          rowData.map(entry => {
            // transform each object as needed
          }); 
        ) 
      );
  }
}

Accessing Angular's Observable Objects

Answer №1

Displaying Observable data in the template

Data Transformation

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