[SOLVED] Function lacks ending return statement and return type does not include 'undefined'

Issue

Function lacks ending return statement and return type does not include ‘undefined’.

In the following async await function I had return type of Promise: <any> but I wanted to correct that so I did the following:

export const getMarkets = async (): Promise<IGetMarketsRes> => {
  try {
    const nomicsUSD = prepHeaders('USD');
    const marketUSD = await nomicsUSD.get(exchangeMarketPrices);
    const nomicsUSDC = prepHeaders('USDC');
    const marketUSDC = await nomicsUSDC.get(exchangeMarketPrices);
    const nomicsUSDT = prepHeaders('USDT');
    const marketUSDT = await nomicsUSDT.get(exchangeMarketPrices);

    console.log('marketUSD', marketUSD);

    return {
      marketUSD: marketUSD.data,
      marketUSDC: marketUSDC.data,
      marketUSDT: marketUSDT.data
    }
  } catch (err) {
    console.error(err);
  }
}

However that creates the error above.

Where getMarkets is called:

export const fetchMarketPrices = (asset: string) => (dispatch: any) => {
  dispatch(actionGetMarketPrices);
  return getMarkets().then((res) => {
    const { marketUSD, marketUSDC, marketUSDT } = res;
    const combinedExchanges = marketUSD.concat(marketUSDC).concat(marketUSDT);
    const exchangesForAsset = combinedExchanges.filter((marketAsset: IMarketAsset) =>
      marketAsset.base === asset);
    return dispatch(actionSetMarketPrices(exchangesForAsset));
  });
}

What is/are the proper Types for that Promise<> syntax?

---

I also tried this which I expected to be the correct way, but got a missing return for Promise, but this is an async await function which is why the return is in the try statement:

export const getMarkets = async (): Promise<IGetMarketsRes> => {

Solution

Solution to keep the try catch

export const getMarkets = async (): Promise<IGetMarketsRes | undefined> => {
  try {
    const nomicsUSD = prepHeaders('111');
    const marketUSD = await nomicsUSD.get(exchangeMarketPrices);
    const nomicsUSDC = prepHeaders('222');
    const marketUSDC = await nomicsUSDC.get(exchangeMarketPrices);
    const nomicsUSDT = prepHeaders('333');
    const marketUSDT = await nomicsUSDT.get(exchangeMarketPrices);

    const { data: dataUSD } = marketUSD;
    const { data: dataUSDC } = marketUSDC;
    const { data: dataUSDT } = marketUSDT;

    if (R.isEmpty(dataUSD) || R.isEmpty(dataUSDC) || R.isEmpty(dataUSDT)) {
      console.error('Market data unavailable');
    }

    return {
      marketUSD: marketUSD.data,
      marketUSDC: marketUSDC.data,
      marketUSDT: marketUSDT.data
    }
  } catch (error) {
    console.error(error);
  }
}

A Much better DRY example

https://codereview.stackexchange.com/questions/213909/get-an-array-of-currency-exchange-prices-based-on-asset

export const fetchMarket = async (currency: string): Promise<any> => {
  try {
    const request = prepHeaders(currency);
    const response =  await request.get(EXCHANGE_MARKET_PRICES);
    if (!response) {
      throw new Error('USD Markets unavailable.');
    }
    return response.data;
  }
  catch(err) {
    console.error(err);
  }
}

// GET Market prices
// http://docs.nomics.com/#operation/getMarkets
export const getMarkets = async (): Promise<IGetMarketsRes | undefined> => {
  try {
    const markets: IMarketRes = {};

    for (let currency of BASE_CURRENCIES) {
      const key = 'market' + currency;
      markets[key] = await fetchMarket(currency);
    }

    return {
      marketUSD: markets['marketUSD'],
      marketUSDC: markets['marketUSDC'],
      marketUSDT: markets['marketUSDT'],
    }
  } catch (error) {
    console.error(error);
  }
}

---

And the call from the actions file:

// Fetch USD, USDC & USDT markets to filter out Exchange List.
export const fetchMarketPrices = (asset: string) => (dispatch: any) => {
  dispatch(actionGetMarketPrices);
  return getMarkets().then((res) => {
    if (res) {
      const exchangesForAsset = combineExchangeData(asset, res);
      return dispatch(actionSetMarketPrices(exchangesForAsset));
    }
  });
}

Answered By – Leon Gaban

Answer Checked By – Marilyn (BugsFixing Volunteer)