Get COMP APY for USDT. Uses Node.js with Compound.js. Be sure to fill in your Infura project ID at the top. See comments for run instructions.

getCompApy.js

const Compound = require('@compound-finance/compound-js');

const provider = 'https://mainnet.infura.io/v3/<YOUR INFURA API KEY HERE>';

const cTokenToGetCompApy = Compound.cUSDT;
const underlying = cTokenToGetCompApy.slice(1, 10);
const underlyingDecimals = Compound.decimals[underlying];
const cTokenDecimals = 8; // always 8
const comptroller = Compound.util.getAddress(Compound.Comptroller);
const opf = Compound.util.getAddress(Compound.PriceFeed);
const cTokenAddr = Compound.util.getAddress(cTokenToGetCompApy);
const apxBlockSpeedInSeconds = 13.15;

const compound = new Compound(provider);

(async function() {

  let compSpeed = await Compound.eth.read(
    comptroller,
    'function compSpeeds(address cToken) public returns (uint)',
    [ cTokenAddr ],
    { provider }
  );

  let compPrice = await compound.getPrice(Compound.COMP, underlying);

  let totalBorrows = await Compound.eth.read(
    cTokenAddr,
    'function totalBorrowsCurrent() returns (uint)',
    [],
    { provider }
  );

  let totalSupply = await Compound.eth.read(
    cTokenAddr,
    'function totalSupply() returns (uint)',
    [],
    { provider }
  );

  let exchangeRate = await Compound.eth.read(
    cTokenAddr,
    'function exchangeRateCurrent() returns (uint)',
    [],
    { provider }
  );

  // Total supply needs to be converted from cTokens
  exchangeRate = +exchangeRate.toString() / Math.pow(10, 18);

  compSpeed = compSpeed / 1e18; // COMP has 18 decimal places
  compPrice = compPrice;  // price feed is USD price with 6 decimal places
  totalBorrows = +totalBorrows.toString() / (Math.pow(10, underlyingDecimals));
  totalSupply = (+totalSupply.toString() * exchangeRate) / (Math.pow(10, underlyingDecimals));

  console.log('compSpeed:', compSpeed);
  console.log('compPrice:', compPrice);
  console.log('totalBorrows:', totalBorrows);
  console.log('totalSupply:', totalSupply);
  console.log('exchangeRate:', exchangeRate);

  const compPerDay = compSpeed * parseInt((60 * 60 * 24) / apxBlockSpeedInSeconds);

  const compBorrowApy = +(100 * (Math.pow((1 + (compPrice * compPerDay / totalBorrows)), 365) - 1)).toFixed(2);
  const compSupplyApy = +(100 * (Math.pow((1 + (compPrice * compPerDay / totalSupply)), 365) - 1)).toFixed(2);

  console.log('compBorrowApy', compBorrowApy, '%');
  console.log('compSupplyApy:', compSupplyApy, '%');

})().catch(console.error);