Typescript Can't implement generic function interface

Question

I'm trying to implement a generic function interface and I cannot make it work.

IToken.ts

export interface IToken {
  token: string;
  expires: number;
}

ITokenMapper.ts

export interface ITokenMapper {
  <T>(apiResult: any): T;
}

tokenMapper.ts

import {ITokenMapper} from "./interfaces/ITokenMapper";
import {IToken} from "./interfaces/IToken";

export const tokenMapper: ITokenMapper = function <IToken>(apiResult: any): IToken {
  if(apiResult.token && apiResult.expires) {
    return {token: apiResult.token as string, expires: apiResult.expires as number}
  }
  throw new Error('Unable to parse token');
};

Here is a screenshot from tokenMapper.ts saying IToken import is unused but I should have a use for it:

tokenMapper.ts

Edit : Using Typescript 3.0.3

Try to avoid using any at best. I also do not understand why you use type hinting in your tokenMapper. What do you want to achieve? — k0pernikus
– k0pernikus, Commented Sep 19, 2018 at 13:26
@k0pernikus I'd create a generic micro application where we could parse result from api token request to a personal interface — AdMer
– AdMer, Commented Sep 19, 2018 at 13:30
@k0pernikus I don't know, that's to goal of my parser, filter informations from a request and keep token string and when it will expire — AdMer
– AdMer, Commented Sep 19, 2018 at 13:31
Why not create an Interface directly for your apiResponse? — k0pernikus
– k0pernikus, Commented Sep 19, 2018 at 13:32

Joe · Accepted Answer · 2018-09-19 13:38:50Z

4

I believe you can accomplish your typing with a generic interface ITokenMapper<T>

interface IToken {
    token: string;
    expires: number;
}

interface ITokenMapper<T> {
    (apiResult: T): T;
}

const tokenMapper: ITokenMapper<IToken> = function (apiResult) {
    if(apiResult.token && apiResult.expires) {
      return { token: apiResult.token as string, expires: apiResult.expires as number};
    }

    throw new Error('Unable to parse token');
};

From: https://www.typescriptlang.org/docs/handbook/generics.html#generic-types

answered Sep 19, 2018 at 13:38

Joe

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2 Comments

k0pernikus Over a year ago

@AdMer Please add in the comment or as an answer of your own what you did change so that it now fits your use-case, so that others with a similar problem may benefit from it as well.

AdMer Over a year ago

@k0pernikus sure i just did it

AdMer · Accepted Answer · 2018-09-20 07:43:17Z

2

So here is what I changed to make it work

ITokenMapper.ts -> IMapper.ts renamed and updated

export type IMapper<T> = (apiResult: any) => T;

tokenMapper.ts -> abpTokenMapper.ts renamed and updated

import { IMapper } from "../../utils/IMapper";
import { IToken } from "../interfaces/IToken";

export const abpTokenMapper: IMapper<IToken> = (apiResult: any) => {
  if (apiResult.accessToken && apiResult.expireInSeconds) {
    return { token: apiResult.accessToken as string, expires: apiResult.expireInSeconds as number }
  }
  throw new Error('Unable to parse token');
};

answered Sep 20, 2018 at 7:43

AdMer

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