Angular doesn't support this particular type as an injection token

Question

Angular doesn't support this particular type as an injection token

I'm attempting to create a constructor with a type of string, but I keep encountering the following error:

This particular type is not supported as an injection token

@Injectable({providedIn: 'root'})
export class DataService {
     constructor(url:string, private http:HttpClient) { 
     }
}

export class PostService extends DataService {
    constructor(http:HttpClient) {
         super("https://jsonplaceholder.typicode.com/posts",http);
    }
 }

angular typescript

Answer 1

Answer №1

It appears that the issue you are facing is as follows: Compiled with problems:X

ERROR

src/app/services/data.service.ts:14:23 - error NG2003: No suitable injection token for parameter 'url' of class 'DataService'.
  Consider using the @Inject decorator to specify an injection token.

14   constructor(private url: string, private http: HttpClient) {}
                         ~~~

  src/app/services/data.service.ts:14:28
    14   constructor(private url: string, private http: HttpClient) {}
                                  ~~~~~~
    This type is not supported as injection token.

The DataService class (which is extended by PostService) should not be marked as injectable. Making a class injectable means it can be provided and injected as a dependency. However, this should not be done in this case as DataService serves the purpose of providing a shape or a reusable service to avoid duplication.

To resolve this issue, you can comment out the Injectable decorator in DataService:

// @Injectable({
//   providedIn: 'root',
// })

export class DataService {
  constructor(private url: string, private http: HttpClient) {}

The revised PostService code should look like this:

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';

import { DataService } from './data.service';

@Injectable({
  providedIn: 'root',
})
export class PostService extends DataService {
  constructor(http: HttpClient) {
    super('https://jsonplaceholder.typicode.com/posts', http);
  }
}

Answer 2

It appears that the issue you are facing is as follows: Compiled with problems:X

ERROR

src/app/services/data.service.ts:14:23 - error NG2003: No suitable injection token for parameter 'url' of class 'DataService'.
  Consider using the @Inject decorator to specify an injection token.

14   constructor(private url: string, private http: HttpClient) {}
                         ~~~

  src/app/services/data.service.ts:14:28
    14   constructor(private url: string, private http: HttpClient) {}
                                  ~~~~~~
    This type is not supported as injection token.

The DataService class (which is extended by PostService) should not be marked as injectable. Making a class injectable means it can be provided and injected as a dependency. However, this should not be done in this case as DataService serves the purpose of providing a shape or a reusable service to avoid duplication.

To resolve this issue, you can comment out the Injectable decorator in DataService:

// @Injectable({
//   providedIn: 'root',
// })

export class DataService {
  constructor(private url: string, private http: HttpClient) {}

The revised PostService code should look like this:

import { HttpClient } from '@angular/common/http';
import { Injectable } from '@angular/core';

import { DataService } from './data.service';

@Injectable({
  providedIn: 'root',
})
export class PostService extends DataService {
  constructor(http: HttpClient) {
    super('https://jsonplaceholder.typicode.com/posts', http);
  }
}

Answer 3

Answer №2

The main concern here is that when DataService is annotated with @Injectable, all constructor parameters must also be injectable, which means that primitive types like string cannot be injected. On the flip side, if PostService is not marked as @Injectable, it will not receive an injected instance of httpClient.

It seems like you don't want DataService to be injectable everywhere, right? Its purpose is to serve as an abstract class, correct?

If that's the case, then you should mark the concrete class(es) as @Injectable:

export abstract class DataService {
     constructor(url:string, private http:HttpClient) { 
     }
}

@Injectable({providedIn: 'root'})
export class PostService extends DataService {
     constructor(http:HttpClient) {
         super("https://jsonplaceholder.typicode.com/posts", http);
     }
 }

Answer 4

The main concern here is that when DataService is annotated with @Injectable, all constructor parameters must also be injectable, which means that primitive types like string cannot be injected. On the flip side, if PostService is not marked as @Injectable, it will not receive an injected instance of httpClient.

It seems like you don't want DataService to be injectable everywhere, right? Its purpose is to serve as an abstract class, correct?

If that's the case, then you should mark the concrete class(es) as @Injectable:

export abstract class DataService {
     constructor(url:string, private http:HttpClient) { 
     }
}

@Injectable({providedIn: 'root'})
export class PostService extends DataService {
     constructor(http:HttpClient) {
         super("https://jsonplaceholder.typicode.com/posts", http);
     }
 }

Answer 5

Answer №3

In my understanding, trying to use the constructor for dependency injection may not be effective in this scenario.

In Angular, subclassing components has always been a bit tricky and fragile, so it's best to avoid it if possible. Instead of inheriting, consider delegating or composing. (Edit: Upon further review, I see that this is not related to a component, my apologies)

However, if you still want to extend, the following approach may work better in your specific case:

export abstract class AbstractDataService {
  constructor(private http: HttpClient) {}

  /** Defined by subclasses. */
  protected abstract getUrl(): string;
}

@Injectable({ providedIn: 'root' })
export class PostService extends AbstractDataService {
  protected getUrl(): string {
    return 'https://jsonplaceholder.typicode.com/posts';
  }
}

Instead of passing the property through the constructor, provide it using an abstract method that you implement in your subclasses.

Answer 6

In my understanding, trying to use the constructor for dependency injection may not be effective in this scenario.

In Angular, subclassing components has always been a bit tricky and fragile, so it's best to avoid it if possible. Instead of inheriting, consider delegating or composing. (Edit: Upon further review, I see that this is not related to a component, my apologies)

However, if you still want to extend, the following approach may work better in your specific case:

export abstract class AbstractDataService {
  constructor(private http: HttpClient) {}

  /** Defined by subclasses. */
  protected abstract getUrl(): string;
}

@Injectable({ providedIn: 'root' })
export class PostService extends AbstractDataService {
  protected getUrl(): string {
    return 'https://jsonplaceholder.typicode.com/posts';
  }
}

Instead of passing the property through the constructor, provide it using an abstract method that you implement in your subclasses.

Angular doesn't support this particular type as an injection token

Answer №1

Answer №2

Answer №3

Similar questions

Issue: Catching errors in proxy function calls

What is the best way to emphasize when the path matches exactly with '/'?

Analysis of cumulative revenue using Palantir Foundry Function

Angular 2 fails to apply active class colors to tabs in a modal popup

Observing changes in the DOM using Angular

Typescript: The art of selectively exporting specific types

Exploring Deeply Nested Routing in Angular

Managing the onChange event for a MaterialUI dropdown component

I'm curious if it's possible to superimpose a png image and specific coordinates onto a map by utilizing react-map

There was a Runtime Error that occurred, stating a TypeError: It is not possible to access properties of an undefined value (specifically

Exploring the differences between initializing class members and using setters and getters in Typescript

The attribute is not found on the combined type

Mapping an array of keys to an array of properties using Typescript

Assets in production encountering a 404 error - distribution glitch

Developing applications using the combination of Vue.js, JSX, and

Dealing with the "expression has changed after it was checked" error in Angular 2, specifically when a component property relies on the current datetime

Saving the compiled Angular dist folder in the artifactory repository

What is the correct placement for the "require("firebase/firestore");" code in my Angular 4 project?

Sending nested JSON in Angular 2 Post Request

Tips for utilizing an elective conversion by typing