The initial iteration of Angular 2 may result in undefined strings

When attempting to retrieve an object from the server using http.get, I am encountering an issue where the strings remain undefined during the first iteration. View the full object

The integers are functioning correctly, but there is a problem with the strings.

        this.http.get("/Home/getRoom", { headers: headers }).map(res => res.json()).subscribe(q => {
    this.timecount = q.timeperquestion; 
    this.player1id = JSON.stringify(q.player1id); 
    this.player2id = q.player2id; 
}, err => console.error(err),
    () => console.log('Complete'));

After the first iteration of the function, the strings are displayed properly.

EDIT:

This is the class:

class AppComponent implements AfterViewInit {
public answered = false;
public title = "loading question...";
public options = [];
public correctAnswer = false;
public working = false;
public timecount=15;
public timer;
public roomID;
public player1id;
public player2id;

constructor(@Inject(Http) private http: Http, private Ref: changeDetectorRef) {


}


nextQuestion() {

    this.working = true;
    this.answered = false;
    this.title = "loading question...";
    this.options = [];
    var headers = new Headers();
    headers.append('If-Modified-Since', 'Mon, 27 Mar 1972 00:00:00 GMT');
    this.http.get("/Home/getRoom", { headers: headers }).map(res => res.json()).subscribe(q => {
    this.timecount = q.timeperquestion;
    this.player1id = JSON.stringify(q.player1id);
    this.Ref.detectChanges();
    },
        err => console.error(err),
        () => console.log('Complete'));

EDIT 2: It appears that everything is functioning correctly with the strings. When attempting to display them using {{player1id}}, the correct value is shown even during the first iteration. The slight "problem" lies in using console.log(player1id) to check the string, as it only displays the correct value after one iteration. Thank you for your assistance!

Answer №1

To trigger the change detection process, you can utilize the ChangeDetectorRef class. Simply inject it into your component and then call its detectChanges method:

constructor(private cdr: ChangeDetectorRef) {
}

updateData() {
  this.authService.getData().subscribe(response => {
    this.data = response;
    this.cdr.detectChanges();
  },
  error => console.error(error),
  () => console.log('Request complete'));
}

Answer №2

The reason why the properties are showing as undefined is because they have not been defined yet. To fix this, you can set them to an empty string like so = "" or explicitly declare their type as a : string similar to the example below:

class AppComponent implements AfterViewInit {
   public player1id: string;
   public player2id = ""; // I personally prefer this method as it initializes the value
   // Code omitted for brevity...
}

When working with TypeScript, it's important to either specify the data type you intend to use or provide a value that allows TypeScript to infer the type. Failing to do so means missing out on all the benefits that TypeScript has to offer.

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