object returned for uint256 return value

Question

I implemented a method to retrieve a price for a currency via some chainlink price feed. This price is casted to an uint256. But if I call this method via etherscan it does not show a number, but just "object Object". Whats the reason for this and how can I get a number to show up here?

function getLatestPrice(address currencyAddress) public view returns (uint256) {
    (, int price, , , ) = priceFeeds[currencyAddress].latestRoundData();

    return uint256(price * 1e10); // Price comes with 8 digits but we need 18
}

Answer 1

I created a contract with the following code and deployed it to the goerli testnet at this address 0x7cEd02A72d311d7734dEF293D520752BA6CcFc02.

Contract example:

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@chainlink/contracts/src/v0.8/interfaces/AggregatorV3Interface.sol";

contract ReturnPriceContract {

    mapping (address => AggregatorV3Interface) public priceFeeds;
    constructor() {
        // LINK/USD price feed on goerli
        priceFeeds[0x45442CB17bD3E3C0AeaE92BF425473E582d5e740] = AggregatorV3Interface(0x48731cF7e84dc94C5f84577882c14Be11a5B7456);
    }

    function getLatestPrice(address currencyAddress) public view returns (uint256) {
    AggregatorV3Interface priceFeed = priceFeeds[currencyAddress];
    require(address(priceFeed) != address(0), "Price feed not found");

    (, int price, , , ) = priceFeed.latestRoundData();
    require(price > 0, "Invalid price");

    uint256 scaledPrice = uint256(price) * 1e10;
    return scaledPrice;
}
}

ethers.js example:

Then I created a quick Node.js script with ethers to fetch the price from getLatestPrice for the LINK token on goerli, to show the returned value as a string:

const ethers = require("ethers");

const provider = new ethers.providers.JsonRpcProvider(
  "https://goerli.infura.io/v3/<api-key>"
);

const abi = [
  "function getLatestPrice(address currencyAddress) public view returns (uint256)",
];

// contract address for ReturnPriceContract deployed on goerli
const contractAddress = "0x7cEd02A72d311d7734dEF293D520752BA6CcFc02";
const contract = new ethers.Contract(contractAddress, abi, provider);

async function main() {
  const price = await contract.getLatestPrice(
    "0x45442CB17bD3E3C0AeaE92BF425473E582d5e740"
  );
  // this returns at the time of writing "8216626120000000000"
  console.log(price.toString());
}

main();

Etherscan Goerli example:

Additionally, I verified the contract 0x7cEd02A72d311d7734dEF293D520752BA6CcFc02 on the goerli testnet - if I read the getLatestPrice for 0x45442CB17bD3E3C0AeaE92BF425473E582d5e740 on the goerli etherscan contract page, you will see the LINK price returned as uint on etherscan.

Hope this helps!