Dealing with 'TypeError X is Not a Function' Error in Angular (TypeScript): Occurrences in Certain Scenarios and Absence in Others

Recently, I came across an odd issue in Angular 14 where a type error kept popping up. Although I managed to refactor the code and find a workaround, I'm quite intrigued as to why this issue is happening so that I can prevent it from occurring again in the future.

The specific error message I am encountering is: ERROR TypeError: this.httpService.user_getUserInfo is not a function

This error seems to be originating from a file named user.service.ts.

Below, you'll see a simplified example of the relevant code (omitting imports and unnecessary details).

@Injectable({
  providedIn: 'root'
})
export class UserService {

constructor(private httpService: HttpService) { }

 getUserInfo(user: string): Observable<UserInfo> {
    return this.httpService.user_getUserInfo(user);
  }

}

What adds to the confusion is that this error doesn't occur in all instances.

I've spent some time experimenting with this today and observed that:

  • If I move the mentioned functionality to another file named users.service.ts (plural form), the error vanishes and everything functions as expected.

  • Conversely, if I copy the code from users.service.ts back to user.service.ts, nothing seems to work (indicating a problem with the file itself rather than the code).

  • Transferring all the functionality to a fresh file named test.service.ts didn't resolve the issue either.

  • Even changing the filename did not rectify the problem.

  • In our other applications where we have a service file named user.service.ts, there are no errors despite similarities in the code.

  • All imports related to user.service.ts are correct in various files.

  • This issue doesn't seem to be related to caching problems in Angular, the browser, or Visual Studio Code.

Has anyone else encountered a similar problem before?

Thank you.

Kevin

Answer №1

Addressing the issue of 'TypeError X is Not a Function' in Angular (TypeScript) - I am deeply appreciative of Naren Murali for pointing me towards the solution. Initially, I was skeptical that imports could be the culprit as I diligently checked and rechecked the file relationships.

Following Naren's advice, I meticulously scrutinized each import and conducted further tests. Despite having accurate imports, I unearthed the root cause of the error to be circular logic within the application.

In this scenario, user.service.ts depended on http.service.ts as a provider while http.service.ts registered user.service.ts as a provider in return. This interconnectedness resulted from an orchestration call made in http.service.ts for user information, subsequently passed back to user.service.ts for additional processing.

Fundamentally, both services were interdependent on each other.

To prevent such occurrences in the future, I intend to refactor the code thoroughly.

Once again, a heartfelt thank you to Naren Murali, and I hope this explanation proves beneficial to others experiencing similar issues :)

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