The Type X is lacking essential properties found in Type Y, including length, pop, push, concat, and an additional 26 more properties. Code: [2740]

Question

The Type X is lacking essential properties found in Type Y, including length, pop, push, concat, and an additional 26 more properties. Code: [2740]

One interesting thing I have noticed is the Product interface:

export interface Product{
  code: string;
  description: string;
  type: string;
}

There is a service with a method that calls the product endpoint:

public getProducts(): Observable<Product> {
    return this.http.get<Product>(`api/products/v1/`);
  }

Then there is a component where the service is used to fetch the Products.

export class ShopComponent implements OnInit {
    public productsArray: Product[];
    
    ngOnInit() {
        this.productService.getProducts().subscribe(res => {
          this.productsArray = res;
        });
    }
}

However, an error occurs with this setup:

[ts] Type 'Product' is missing the following properties from type 'Product[]': length, pop, push, concat, and 26 more. [2740]

If the typing on productsArray variable is removed, the error goes away. But it's puzzling why this doesn't work, considering the server response is an array of objects of type Products.

angular typescript typescript-typings

Answer 1

Answer №1

When you return Observable<Product>, it is expected to be Product[] within the subscribe callback.

The types returned from http.get() and getProducts() should both be Observable<Product[]>

public getProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`api/products/v1/`);
}

Answer 2

When you return Observable<Product>, it is expected to be Product[] within the subscribe callback.

The types returned from http.get() and getProducts() should both be Observable<Product[]>

public getProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`api/products/v1/`);
}

Answer 3

Answer №2

It appears that you may have overlooked specifying the return type of getProducts as an array. The current implementation suggests it will only return a single product. To rectify this, ensure the following code is updated:

public fetchAllProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`api/products/v1/`);
  }

Answer 4

It appears that you may have overlooked specifying the return type of getProducts as an array. The current implementation suggests it will only return a single product. To rectify this, ensure the following code is updated:

public fetchAllProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`api/products/v1/`);
  }

Answer 5

Answer №3

Here's a tip for beginners like myself: avoid assigning variables to service responses in your code.

export class ShopComponent implements OnInit {
  public productsArray: Product[];

  ngOnInit() {
      this.productService.getProducts().subscribe(res => {
        this.productsArray = res;
      });
  }
}

Instead of doing something like this:

export class ShopComponent implements OnInit {
    public productsArray: Product[];

    ngOnInit() {
        this.productsArray = this.productService.getProducts().subscribe();
    }
}

Answer 6

Here's a tip for beginners like myself: avoid assigning variables to service responses in your code.

export class ShopComponent implements OnInit {
  public productsArray: Product[];

  ngOnInit() {
      this.productService.getProducts().subscribe(res => {
        this.productsArray = res;
      });
  }
}

Instead of doing something like this:

export class ShopComponent implements OnInit {
    public productsArray: Product[];

    ngOnInit() {
        this.productsArray = this.productService.getProducts().subscribe();
    }
}

Answer 7

Answer №4

Please indicate the type of response you are expecting:

this.productService.getProducts().subscribe(res => {
    this.productsArray = res;
});

Consider using this instead:

this.productService.getProducts().subscribe((res: Product[]) => {
    this.productsArray = res;
});

Answer 8

Please indicate the type of response you are expecting:

this.productService.getProducts().subscribe(res => {
    this.productsArray = res;
});

Consider using this instead:

this.productService.getProducts().subscribe((res: Product[]) => {
    this.productsArray = res;
});

Answer 9

Answer №5

Encountering the same issue led me to devise a solution that involved defining an interface similar to this:

export class Alert {
    id: number;
    title: string;
    description: string;
}

In the alertService component, I implemented the following:

allAlerts: Alert[]; 
  //AlertDetail: Alert;  
  private alertsUrl = 'assets/data/alert.json';  
  private feedsUrl = 'assets/data/feed.json';  

  constructor(private httpClient: HttpClient ) { }

  getAlerts(): Observable<Alert[]> {    
       return this.httpClient.get<Alert[]>

(this.alertsUrl).pipe(map(res => this.allAlerts = res))
      }

Lastly, in the corresponding component:

 constructor(private alertService: AlertService) {
   }

  ngOnInit() {
      /* Retrieve Alerts */
      this.alertService.getAlerts().subscribe(data => this.alerts = data);
}

Answer 10

Encountering the same issue led me to devise a solution that involved defining an interface similar to this:

export class Alert {
    id: number;
    title: string;
    description: string;
}

In the alertService component, I implemented the following:

allAlerts: Alert[]; 
  //AlertDetail: Alert;  
  private alertsUrl = 'assets/data/alert.json';  
  private feedsUrl = 'assets/data/feed.json';  

  constructor(private httpClient: HttpClient ) { }

  getAlerts(): Observable<Alert[]> {    
       return this.httpClient.get<Alert[]>

(this.alertsUrl).pipe(map(res => this.allAlerts = res))
      }

Lastly, in the corresponding component:

 constructor(private alertService: AlertService) {
   }

  ngOnInit() {
      /* Retrieve Alerts */
      this.alertService.getAlerts().subscribe(data => this.alerts = data);
}

Answer 11

Answer №6

Encountered a similar issue with my GraphQL mutation input object, but managed to identify the root cause. In my scenario, the mutation expected an array of objects as input, whereas I mistakenly attempted to insert a single object. Here is a comparison of the erroneous and corrected mutation calls:

Erroneous attempt

const mutationName = await apolloClient.mutate<insert_mutation, insert_mutationVariables>({
      mutation: MUTATION,
      variables: {
        objects: {id: 1, name: "John Doe"},
      },
    });

Corrected version using an array

const mutationName = await apolloClient.mutate<insert_mutation, insert_mutationVariables>({
      mutation: MUTATION,
      variables: {
        objects: [{id: 1, name: "John Doe"}],
      },
    });

Simple oversights like this can lead to unexpected errors. Sharing in case it helps someone facing a similar issue.

Answer 12

Encountered a similar issue with my GraphQL mutation input object, but managed to identify the root cause. In my scenario, the mutation expected an array of objects as input, whereas I mistakenly attempted to insert a single object. Here is a comparison of the erroneous and corrected mutation calls:

Erroneous attempt

const mutationName = await apolloClient.mutate<insert_mutation, insert_mutationVariables>({
      mutation: MUTATION,
      variables: {
        objects: {id: 1, name: "John Doe"},
      },
    });

Corrected version using an array

const mutationName = await apolloClient.mutate<insert_mutation, insert_mutationVariables>({
      mutation: MUTATION,
      variables: {
        objects: [{id: 1, name: "John Doe"}],
      },
    });

Simple oversights like this can lead to unexpected errors. Sharing in case it helps someone facing a similar issue.

Answer 13

Answer №7

The reason behind the error I encountered was due to an incorrect type hint for the URL string. Initially, I mistakenly used:

export class TodoService {

  apiUrl: String = 'https://jsonplaceholder.typicode.com/todos' // erroneously capitalized String

  constructor(private httpClient: HttpClient) { }

  getTodos(): Observable<Todo[]> {
    return this.httpClient.get<Todo[]>(this.apiUrl)
  }
}

Instead, the correct approach should have been:

export class TodoService {

  apiUrl: string = 'https://jsonplaceholder.typicode.com/todos' // proper lowercase string declaration

  constructor(private httpClient: HttpClient) { }

  getTodos(): Observable<Todo[]> {
    return this.httpClient.get<Todo[]>(this.apiUrl)
  }
}

Answer 14

The reason behind the error I encountered was due to an incorrect type hint for the URL string. Initially, I mistakenly used:

export class TodoService {

  apiUrl: String = 'https://jsonplaceholder.typicode.com/todos' // erroneously capitalized String

  constructor(private httpClient: HttpClient) { }

  getTodos(): Observable<Todo[]> {
    return this.httpClient.get<Todo[]>(this.apiUrl)
  }
}

Instead, the correct approach should have been:

export class TodoService {

  apiUrl: string = 'https://jsonplaceholder.typicode.com/todos' // proper lowercase string declaration

  constructor(private httpClient: HttpClient) { }

  getTodos(): Observable<Todo[]> {
    return this.httpClient.get<Todo[]>(this.apiUrl)
  }
}

Answer 15

Answer №8

This issue may arise if you are neglecting to subscribe to the Observable.

For instance, rather than:

this.items = this.itemService.getItems();

try:

   this.itemService.getItems().subscribe({
    next: items=>this.items = items,
    error: err=>this.errorMessage = err
   });

Answer 16

This issue may arise if you are neglecting to subscribe to the Observable.

For instance, rather than:

this.items = this.itemService.getItems();

try:

   this.itemService.getItems().subscribe({
    next: items=>this.items = items,
    error: err=>this.errorMessage = err
   });

The Type X is lacking essential properties found in Type Y, including length, pop, push, concat, and an additional 26 more properties. Code: [2740]

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

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