Having trouble retrieving the return value from an Angular HTTP POST request?

My current project involves developing an Angular frontend that will handle multiple HTTP POST requests. The data is sent to the backend, which then responds with a confirmation. While the first part of the process is working smoothly, I'm encountering an issue when trying to access the returned data. Despite confirming that the backend is functioning correctly using Postman, I keep encountering 'Undefined' when trying to assign the data to a variable on the frontend. Here is a snippet of my code:

Method 1:

 onSubmitP1()
  {
    const formData = new FormData();
    formData.append('data_selection', this.SearchDataForm.get('dataselection').value);

    console.dir(this.SearchDataForm.get('dataselection').value);

    let headerOptions = new HttpHeaders();
    headerOptions.append('Content-Type', 'application/text; charset=UTF-8');

    return this.httpClient.post(this.SERVER_URL, formData, {headers: headerOptions});
  }

Method 2:

onSubmitP2()
  {
    this.onSubmitP1().subscribe((data) => this.result = data);

    console.log(this.result);
    console.dir(this.result);
  }

When the HTML submit button is pressed, Method 2 is called first, which in turn triggers Method 1 to make the POST request and return the observable value. The goal is to assign the data returned by the web service to the variable "result" for viewing, but the value keeps returning as 'undefined'.

Answer №1

The main issue lies in grasping the concept of asynchronous code, particularly in the realm of JS/TS. The lines within the console are executed before any data is returned, since the subscription hasn't produced any results yet. I highly recommend delving into the intricacies of asynchronous code in the field of Web development. As a quick fix, you can try the following workaround:

this.onSubmitP1().subscribe((data) => {
  this.result = data;
  // handle result operations here
});

Answer №2

try a different approach like this

onSubmitP2()
  {
    this.onSubmitP1().subscribe((data) => {
     this.result = data

     console.log(this.result);
     console.dir(this.result);
    });

  }

I have added console logs inside the callback function that executes after the result is received. Your original version logs were being called immediately after the call was made, not after it was completed. This is due to the asynchronous nature of JavaScript.

Answer №3

Accessing this information is like trying to predict the future ;) The function you subscribed to will be executed once the server has a response ready, as it is an asynchronous call. This means that any code you write after the call will run first before the function completes.

Answer №4

When calling onSubmitP2(), make sure that it subscribes to the onSubmitP1() method correctly. Currently, the code sets this.result = data at the end of the Async call (essentially at the end of the Http request), but it logs to the console immediately. To fix this, adjust your subscription logic:

onSubmitP2()
  {
    this.onSubmitP1().subscribe((data) => { 

       this.result = data;

       console.log(this.result);
       console.dir(this.result);

    });
  }

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