How to use abstract class in typescript?

Question

In the following code, I'm getting an error on implementing the abstract method getPrice.

abstract class Exchange {
    public coins=[];
    abstract getPrice();
}
class Binance extends Exchange {
    getPrice(coin,stable_coin){
       return  axios.get(`https://api.binance.com/api/v3/avgPrice?symbol=${coin.symbol}${stable_coin.symbol}`).then(res=>res.data.price)
    }
}
class Bittrex extends Exchange {
    getPrice(coin,stable_coin){
        return  axios.get(`https://api.bittrex.com/api/v1.1/public/getticker?market=${stable_coin.symbol}-${coin.symbol}`).then(res=>res.data.result.Last);
     }
}

I'm getting the following error:

Property 'getPrice' in type 'Binance' is not assignable to the same property in base type 'Exchange'. Type '(coin: any, stable_coin: any) => any' is not assignable to type '() => any'.ts(2416)

d.moncada · Accepted Answer · 2022-01-12 02:02:51Z

2

You need to match the parameters of the abstract method as well. your derived classes are passing arguments that arent defined in the base class.

abstract class Exchange {
    public coins=[];
    abstract getPrice(coin:any, stable_coin: any): any;
}
class Binance extends Exchange {
    getPrice(coin: any, stable_coin: any): any {
       return  axios.get(`https://api.binance.com/api/v3/avgPrice?symbol=${coin.symbol}${stable_coin.symbol}`).then(res=>res.data.price)
    }
}
class Bittrex extends Exchange {
    getPrice(coin: any, stable_coin: any): any {
        return  axios.get(`https://api.bittrex.com/api/v1.1/public/getticker?market=${stable_coin.symbol}-${coin.symbol}`).then(res=>res.data.result.Last);
     }
}

answered Jan 12, 2022 at 2:02

d.moncada

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Comments

ghybs · Accepted Answer · 2022-01-12 02:05:59Z

1

This is a common class inheritance expectation: overriding methods should have a compatible signature with the base (super) method.

Here you could have e.g. abstract getPrice(coin: any, stable_coin: any) in your abstract class.

Or, depending if it makes sense in your case or not, have the extra parameters of your child methods be optional.

answered Jan 12, 2022 at 2:05

ghybs

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