Angular4 and TypeScript compile error TS2453

Question

I cannot build my Angular4 project because of that error that I really don't understand. I have my imports like Response, Headers, Http from @angular. When I'm trying to build my project I get this error:

TS2453: The type argument for type parameter 'T' cannot be inferred from the usage. Consider specifying the type arguments explicitly. Type argument candidate 'Response' is not a valid type argument because it is not a supertype of candidate 'Response'. Types of property 'type' are incompatible. Type 'string' is not assignable to type 'ResponseType'.

It refers to this code:

public getPatients(): Observable<any> {
    //noinspection TypeScriptValidateTypes
    return this.http.get(AppSettings.API_ENDPOINT + 'patient', { headers: this.getHeaders() })
        .map((res:Response) => res.json())
        .catch((error) => Observable.throw(error.json().error || "Server error"));
}

I found a workaround with imports and I added all mentioned in those threads but it still doesn't help.

Can you split your return statement, introducing a variable for the http.get().map(), and tell us what line produces the error? I suspect the inferred type of the returned value of the catch(). — Romain Deneau
– Romain Deneau, Commented Oct 1, 2017 at 11:42

Adi Purcaru · Accepted Answer · 2017-11-06 20:27:50Z

2

I had the same problem and i found out that the problem was that i did not import the right things.

try using these :

import {Http, Response} from "@angular/http";
import 'rxjs/add/operator/map'
import 'rxjs/add/operator/catch';
import {Observable } from "rxjs/Observable";

answered Nov 6, 2017 at 20:27

Adi Purcaru

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Adrien PESSU · Accepted Answer · 2017-09-30 14:53:55Z

0

If have code like this :

editItem(item: Item) {
    return this.http.put(`${this.BACKOFFICE_URL}`, item, this.getOptions())
        .map((res: Response) => {
            return res.status === 200 ? res.json() : {};
        })
        .catch((error: any) => {
            return Observable.throw(error);
        })
}

The only difference I see with your code is that I don't put a return type to the function.

answered Sep 30, 2017 at 14:53

Adrien PESSU

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