The variable "this.data" in Angular 2 is experiencing the issue

I am attempting to access and read the information stored in my JSON file using my "GetJsonService".

app.component.ts:

data: any;

constructor(private jsonService: GetJsonService) {}

ngOnInit() {
    this.getRecords();
    console.log(this.data);
}

getRecords() {
    this.jsonService.retrieveRecords().subscribe(data => {
        this.data = data;
    }, err => {
        console.log(err);
    });
}

get-json.service.ts

constructor(private http: Http) { }

data: any;

retrieveRecords() {
    return this.http.get('assets/standorte.json').map(data => {
        this.data = data.json();
        return data.json();
    }, err => {
        if (err) {
            return err.json();
       }
     });
 }

I aim to assign the contents of data.json() to this.data for further use. However, when I output this.data, it shows as "undefined".

I am fairly new to Angular 2 and Typescript, so I would greatly appreciate any assistance.

Best regards!

Answer №1

Big thanks to @MauricioSipmann for coming through and helping me solve my issue. I was dealing with asynchronous code execution in a request, something I was aware of but Typescript added some confusion to the mix.

Appreciation goes out to everyone who responded!

Answer №2

Adjust your getRecords() method like this:

Here is the updated code snippet:

getRecords() {
    this.jsonService.getRecords().subscribe(data => {
        this.data = data;
        console.log(this.data);
    }, err => {
        console.log(err);
    });
}

Rather than logging after calling the method, make sure to log inside the success callback of the service.

This issue is commonly encountered by developers when starting with Angular 2+. This is because it involves an async call, where the console.log() statement executes before the value this.data = data; is assigned by the service.

If you display the data in the HTML using your current code, it should work correctly. The confusion arises from the incorrect logging behavior.

Answer №3

There is no need to convert to json when using Angular 6. Simply return the request as it is.

fetchData() {
  return this.http.get('assets/locations.json') 
}

Answer №4

One issue that needs to be addressed is the lack of re-throwing the async state in your code. Here's a suggestion:

ngOnInit() {
    this.fetchData().then((response) => {
        console.log(response);
    });
}

fetchData() {
    return new Promise((resolve, reject) => {
        this.apiService.fetchData().subscribe(
            data => {
                this.data = data;
                resolve(data);
            }, 
            error => {
                console.log(error);
                reject(error);
            }
        );
    });
}

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