Duplicate function implementation in Typescript

Question

I am writing an adapter for the HttpClient from Angular and I need two distinct get functions. One that returns a Blob and one that returns a generic. But when I try to implement it, I get the error:

TS2393: Duplicate function implementation.

  get<T>(url: string, options?: {
    headers?: HttpHeaders | {
      [header: string]: string | string[];
    };
    context?: HttpContext;
    observe?: 'body';
    params?: HttpParams | {
      [param: string]: string | number | boolean | ReadonlyArray<string | number | boolean>;
    };
    reportProgress?: boolean;
    responseType?: 'json';
    withCredentials?: boolean;
  }): Observable<T> {
    return this.handleRequest(this.http.get<T>(url, options));
  }

  get(url: string, options: {
    headers?: HttpHeaders | {
      [header: string]: string | string[];
    };
    observe: 'response';
    context?: HttpContext;
    params?: HttpParams | {
      [param: string]: string | number | boolean | ReadonlyArray<string | number | boolean>;
    };
    reportProgress?: boolean;
    responseType: 'blob';
    withCredentials?: boolean;
  }): Observable<HttpResponse<Blob>> {
    return this.handleRequest(this.http.get(url, options));
  }

I don't understand that this is an error when the actual implementation of the get functions in the HttpClient class looks almost the same.

Mike Jerred · Accepted Answer · 2022-06-23 14:57:43Z

1

You cannot have two functions with the same name (and within the same scope) in javascript. You must instead make a single function that can work out which arguments you have and do the right thing, then with typescript you can write two different function signatures to get the types correct e.g.:

get<T>(url: string, observe: 'body'): Observable<T>;
get(url: string, observe: 'response'): Observable<HttpResponse<Blob>>;
get(url: string, observe: 'body' | 'response') {
  if (observe === 'body') {
    // ... implementation
  } else {
    // ... implementation
  }
}

edited Jun 23, 2022 at 14:57

answered Jun 23, 2022 at 14:48

Mike Jerred

10.7k5 gold badges25 silver badges48 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Stefan Over a year ago

I mean I get it, since the transpiled javascript would look equal. But somehow it is okay for the HttpClient implementation

Mike Jerred Over a year ago

The HttpClient is implemented here: github.com/angular/angular/blob/… all the ones above are just function delcarations: they have no implementation.

Collectives™ on Stack Overflow

Duplicate function implementation in Typescript

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related