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

Similar questions

Guarding against Angular routes that do not have a component and may include an

Why am I encountering this issue? The "map" property does not appear to be available for the type "Observable<boolean>"

Incorporate a fresh element into an object after its initial creation

Unable to start an expo project in bare workflow using TypeScript

The object might be undefined; TypeScript; Object

The TypeScript function was anticipating one argument, however it received two instead

Display problem with Angular 2 component: dimensions are missing

An issue with the "req" parameter in Middleware.ts: - No compatible overload found for this call

How to perform a fetch on a local path in Next.js?

Error encountered when upgrading to Material-UI v5 rc.0 with typescript

Angular 2 routing malfunctioning

What is the proper way to call document methods, like getElementByID, in a tsx file?

How to retrieve the data from a PHP file using Angular 4 CLI?

An issue arises when using an Observable in the model while employing Angular's dynamic component loading

When sending an HTTP POST request to a Nodejs service with an uploaded file, the request fails after 8-15 seconds on Firefox and 25 seconds on Chrome

Leverage Formidable to directly stream content to Azure Blob Storage without the need to save it in the /tmp directory

Is there any benefit to making the SVG elements width and height 100%?

Troubleshooting issue with Vue3 - TS Custom State Management

Utilizing a string as an index in TypeScript

Implementing Custom Font Awesome Icons in Your Angular Project