Angular HttpClient获取，此对象错误

Question

in my Angular App i make a simple call to a node.js server. the HttpClient "get" function returns the right answer. This answer I want to store in a variable of my component "interfaces". But in the "subscribe" function of the get request my "this" pointer doesn't point to my component. Instead it tells me that it is of type "SafeSubscriber". Any call to my member "interfaces" lead to the following error: TypeError: Cannot read property 'interfaces' of undefined

export class SettingsComponent implements OnInit {

public interfaces : string[];

constructor(private http: HttpClient) {
    this.interfaces = [];
    this.interfaces.push("huhu");

}

ngOnInit() : void {

    this.http.get('http://localhost:3000/settings/interfaces').subscribe((data) => {
        // Read the result field from the JSON response.
        console.log(data);
        this.interfaces.push("xxx");
        Object.keys(data).forEach(function(k) {
            console.log(k);
            this.interfaces.push("xxx");
        });
    }),
    err => {
      console.log("error " + err);
    }; 
}

}

As you can see I also tried to enter some values manually into the array just to make sure, that not the server response is causing the problem. Any help is appreciated.

I used this code as a blueprint which is from: https://angular.io/guide/http

@Component(...)
export class MyComponent implements OnInit {

  results: string[];

  // Inject HttpClient into your component or service.
  constructor(private http: HttpClient) {}

  ngOnInit(): void {
    // Make the HTTP request:
    this.http.get('/api/items').subscribe(data => {
      // Read the result field from the JSON response.
      this.results = data['results'];
    });
  }
}

Answer 1

You're losing reference to the correct this in this statement:

Object.keys(data).forEach(function(k) {..})

Inside the function block code this refers to the calling context , which is the subscribe method itself, that's why interfaces is undefined, since it's not a property of the subscribe method.

You can change the function for a lambda en it should be fine:

Object.keys(data).forEach((k) => {..})