The process of assigning a local variable to a JSON response in Angular 2

I need to store a JSON response that includes an array with the following data:

0 : {ID: 2, NAME: "asd", PWD_EXPIRY_IN_DAYS: 30}

1 : {ID: 1, NAME: "Admin", PWD_EXPIRY_IN_DAYS: 30}

In my code, I have defined a local variable called groups of type Group as shown below:

    export class Group {
    id: string;
    name: string;
    pwd_expiry_in_days: string;
}

The issue arises when I try to assign the JSON response to an object of type Group in my component. The current implementation is not working and displays 'undefined'. Here is the section of code causing the problem:

    import { Injectable, Provider, ModuleWithProviders, Component, OnInit } from '@angular/core';
import { Http, Headers, Response, RequestOptions } from '@angular/http';

import { Observable } from 'rxjs/Observable';
import {Group} from '../../_models/group'
import 'rxjs/add/operator/map';


interface Validator<T extends FormControl> {
  (c: T): { [error: string]: any };
}

@Component({
  selector: 'form1',
  templateUrl: './form1.html',
  moduleId: module.id,
})
export class Form1Component {

  public roles: Group; // <--- variable to feed response into


   private getGroups(): Observable<any> {
    console.log("In Groups");
    var responseAsObject: any;
    let _url = groupsURL";
    let headers = new Headers();
    headers.append('X-User', sessionStorage.getItem('username'));
    headers.append('X-Token', sessionStorage.getItem('token'));
    headers.append('X-AccessTime', sessionStorage.getItem('AccessTime'));
    headers.append('Content-Type', 'application/json');
    let options = new RequestOptions({ headers: headers });

    return this.http.get(_url, options)
    .map(response => {
      var responseAsObject = response.json();
      console.log(responseAsObject); //<--- proper response
      return responseAsObject;
    })
}


  constructor(private http: Http) {

    this.getGroups()
    .subscribe(data => {
      this.roles = data;
      console.log(this.roles); //<--- proper response
    });

    console.log(this.roles); //<----- undefined, I need the roles variable so I can use it on the front end

}

How can I resolve this issue? It seems to be related to an Async problem where simply assigning data to this.roles does not work and results in 'undefined' outside the subscription scope in my component.

What would be the correct approach to assigning a response to my local variable in this scenario?

An updated template has been added to view the object, but it still shows up as undefined:

        <div class="form-group" [ngClass]="{'has-error':!complexForm.controls['group_id'].valid}">
      <label>Group ID</label>
      <div class="row">
        <div class="col-md-4">
          <select name="group_id" id="group_id" class="form-control" [formControl]="complexForm.controls['group_id']" data-width='200px'>
    <option *ngFor="let role of roles" [value]="role.id">  
    {{role.name}}
    </option>
  </select>
        </div>
      </div>
    </div>

Thank you!

Answer №1

How should I properly assign a response to my local variable in this scenario?

You're on the right track. Just ensure that you handle cases where the response may be undefined or empty when the component is initially constructed.

An easy solution is to add an *ngIf="someArray.length" condition to the HTML element before iterating through it, like this:

// html
...
<div class="row" *ngIf="roles.length"><!-- Prevents un-populated array iteration -->
    <div class="col-md-4">
        <select class="form-control">
            <option *ngFor="let role of roles" [value]="role.id">
                {{role.name}}
            </option>
        </select>
    </div>
</div>

You can also make some improvements in your TypeScript code, such as avoiding changing the reference of the array. Instead of this.roles = data, you can do something like

this.roles.length = 0; this.roles.push(...data);
. For more information, refer to Angular Change Detection.

// ts
export class Form1Component implements OnInit{
    public roles: Array<Group> = []; // <--- Shouldn't this be an Array?
    ...
    private getGroups() : Observable<any> {
        var responseAsObject : any;
        ...
        return this.http.get(_url, options)
            .map(response => {
                var responseAsObject = response.json();
                return responseAsObject;
            });
    }

    constructor(private http: Http) {}

    ngOnInit(){
        this.getGroups()
            .subscribe(data => {
                let groups = data.map(item=>{
                                return new Group(item)
                             });//<--- If you want it to be of type `Group`
                this.roles.length = 0;
                this.roles.push(...groups);
            });
    }
    ...
}

Answer №2

It's important to note that the second console log will be executed before the api call due to its asynchronous nature. To address this issue, consider defining the role type as public role: any. If this resolves the issue, you may need to update your Group model accordingly.

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

The attempt to upload a file in Angular was unsuccessful

Below is the backend code snippet used to upload a file: $app->post('/upload/{studentid}', function(Request $request, Response $response, $args) { $uploadedFiles = $request->getUploadedFiles(); $uploadedFile = $uploadedFiles[&apo ...

Angular 4 Bootstrap 4 Collapsible Navigation Bar

Struggling for a while now trying to achieve the exact functionality I desire. Within my Angular Universal App, there is a vertical navigation bar at the top that I want to make responsive for mobile devices. I am utilizing Bootstrap 4 Alpha 6 and ngx-boot ...

Advanced automatic type inference for object literals in TypeScript

When working with TypeScript, I often declare generic functions using the syntax: const fn: <T>(arg: T)=>Partial<T> While TypeScript can sometimes infer the type parameter of a function based on its parameters, I find myself wondering if t ...

angular 17 standalone component utilizing ngrx-store-localstorage

In my angular 17 project, I am utilizing ngrx-store-localstorage to persist my store in localstorage using the new standalone method. Here is how I set up my meta reducer: export function localStorageSyncConfig(): LocalStorageConfig { return { keys: ...

Error Found in Angular2 Console Inspection

So, when I check the webpage inspection console, I see this error: Uncaught SyntaxError: Unexpected token { at Object.<anonymous> (main.bundle.js:3885) at __webpack_require__ (polyfills.bundle.js:51) at eval (eval at <anonymous> (m ...

The associated type 'Iterator' of type 'DecodedArray<T>' is not valid

I am currently attempting to parse data using the tutorial linked below However, I encountered an error: Reference to invalid associated type 'Iterator' of type 'DecodedArray' ** subscript(index: Index) -> Iterator.Element { ...

Encountering issues with accessing properties of undefined while chaining methods

When comparing lists using an extension method that calls a comparer, I encountered an error. Here is the code snippet: type HasDiff<T> = (object: T, row: any) => boolean; export const isListEqualToRows = <T>(objects: T[], rows: any[], has ...

python decoding json using Twisted

Here's the code I've written using the Python Twisted library: class Cache(protocol.Protocol): def __init__(self, factory): self.factory = factory def dataReceived(self, data): request = json.loads(data) self.fac ...

What is causing the question mark symbol to appear at the beginning of my ajax response?

Below is my JavaScript code: $('#tags').select2({ tags: true, tokenSeparators: [','], createSearchChoice: function (term) { return { id: $.trim(term), text: $.trim(term) + ' (new tag)&ap ...

Troubleshooting the error message "TypeError: Cannot read property 'name' of undefined" when working with data binding in Angular 4

I am brand new to Angular and I have been working on creating a custom Component. Specifically, I am trying to display a list of Courses (objects) which consist of two properties: id and name. So far, this logic is functioning properly. However, when attem ...

Step-by-step guide on implementing Form.create in TypeScript and Ant Design with function components

Having trouble compiling my form created using Form.create(). The error message I'm getting is: Argument of type 'FunctionComponent<MyProps>' is not assignable to parameter of type 'ComponentType<{}>'. Type 'Fu ...

Parsing a JSON array and populating a hive table

I have an array in Json format as shown below: [{"Name":"xxxx","Machine":"Machine1"},{"Name":"yyyy","Machine":"Machine2"},{"Name":"zzzz","Machine":"Machine3"}] I am looking to extract and load this data into a hive table structured like this: Name Ma ...

Utilizing Spring's Rest Service in Version 4.x

Despite encountering numerous inquiries on the subject, none have proven helpful to me. I'm attempting to launch a basic REST service, but no matter what I try, it just won't work. My initial approach was to set up a REST controller like this: ...

Ways to navigate a JSON file and automatically populate an ImageView based on the JSON data

Hello, I need help figuring out how to dynamically load ImageView based on the data received from JSON. Sometimes I receive 8 images to display, other times it's 17. The challenge is loading the correct number of ImageViews based on the JSON data. Cur ...

Is a special *ngFor required when implementing Angular2 with Nativescript?

My current project involves creating a mobile app that requires listing a few labels. Here is the code snippet: @Component({ selector: 'code-m', template: ` <StackLayout dock="top" orientation="vertical" style="height: ...

Utilize JSON information on a different JSP webpage

I'm encountering an issue with passing information between two JSP pages. I am unable to display the information in the second page. function sendSuccess (dir) { console.log(jdata); $.ajax({ url: dir, type: "POST", dat ...

Sending a json array from PHP

I spent several hours searching for solutions to my problem but couldn't find an answer. I'm trying to perform a search on the same page using jQuery, AJAX, and PHP. Unfortunately, the array from PHP is still returning undefined. Here is the P ...

What is the process for obtaining the final element in an array of objects when a particular character is present in the value of a key?

Given the following array: arrOfOranges = [{ "kerp": "thisThing", "time": "@ rocks 3"}, { "kerp": "otherThing", "green": "blah"}, { "kerp": "thisThing", "time": "(countriesToTheStart ^"}, { "kerp": "anotherThing", "yellow": "row row"}, { "kerp": "anotherTh ...

Guide on implementing Google sign in functionality in Angular 6 and redirecting on successful sign in

Seeking Clarity I recently implemented a component that presents a Google Sign In button to unauthenticated users. Upon signing in, the access token is sent to my server for verification, which then returns a jsonwebtoken. I followed Google's documen ...

What is causing the geolocation heading to remain "null" on Android devices when using Chrome?

Recently, I developed a compact geolocation watch using the following code snippet: navigator.geolocation.watchPosition( this.updateLocation.bind(this), this.errorLocation.bind(this), {enableHighAccuracy: true} ); The function updateLocation ...