CODEWITHSUNDEEP
typescriptfetch-api
user351711
user351711

Reputation: 3301

TypeScript Fetch response.Json<T> - Expected 0 type arguments, but got 1

forgive my ignorance but I am trying to implement a fetch in TypeScript and I have been going through the examples but cannot get it to compile. I am new to TypeScript and Promise and I found this example:

How to use fetch in typescript

And I am trying to implement this:

private api<T>(url: string): Promise<T> {
        return fetch(url)
          .then(response => {
            if (!response.ok) {
              throw new Error(response.statusText)
            }
            return response.json<T>()
          })          
}

However the compiler shows the error:

[ts] Expected 0 type arguments, but got 1.

I am not sure what the problem is but basically I am trying to implement a class which wraps the API calls to return an array of items and I have experimented with async/await and nothing seems to quite work. Any help would be greatly appreciated.

Upvotes: 18

Views: 23469

Answers (3)

FloatingRock
FloatingRock

Reputation: 7065

Got the same error with Express when I forgot this import:

import { Request, Response } from 'express';

The complete example becomes:

// controllers/my-controller.ts
import { Request, Response } from 'express';

export const someMethod = async (req: Request, res: Response) => {
   // ...
}

Upvotes: 7

Fyodor Yemelyanenko
Fyodor Yemelyanenko

Reputation: 11848

I found one problem with answer above. If you have JSON body like this

{ "error" : "{ "message" : "some message" }" }

code above will return object with one key error and "{ "message" : "some message" }" So it's better to use 

JSON.Stringify(data)

Upvotes: 0

Marco Medrano
Marco Medrano

Reputation: 3040

Seems that signature is not there anymore, Instead use this code:

response.json().then(data => data as T);

Yeah, that will return you a strong typed data. Below the complete code snipped.

private api<T>(url: string): Promise<T> {
    return fetch(url)
      .then(response => {
        if (!response.ok) {
          throw new Error(response.statusText)
        }
        return response.json().then(data => data as T);
      })          
}

Upvotes: 17

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