add how to calculate apy defi

screencast/266-how-to-calculate-apy-defi/apy1.js

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+const Compound = require('@compound-finance/compound-js');
+
+const provider = 'INFURA URL HERE';
+
+const comptroller = Compound.util.getAddress(Compound.Comptroller);
+const opf = Compound.util.getAddress(Compound.PriceFeed);
+
+const cTokenDecimals = 8; // always 8
+const blocksPerDay = 4 * 60 * 24; // 4 blocks in 1 minute
+const daysPerYear = 365;
+const ethMantissa = Math.pow(10, 18); // 1 * 10 ^ 18
+
+async function calculateSupplyApy(cToken, ticker) {
+  const supplyRatePerBlock = await Compound.eth.read(
+    cToken,
+    'function supplyRatePerBlock() returns (uint)',
+    [],
+    { provider }
+  );
+
+  return 100 * (Math.pow((supplyRatePerBlock / ethMantissa * blocksPerDay) + 1, daysPerYear - 1) - 1);
+}
+
+async function calculateCompApy(cToken, ticker, underlyingDecimals) {
+  let compSpeed = await Compound.eth.read(
+    comptroller,
+    'function compSpeeds(address cToken) public returns (uint)',
+    [ cToken ],
+    { provider }
+  );
+
+  let compPrice = await Compound.eth.read(
+    opf,
+    'function price(string memory symbol) external view returns (uint)',
+    [ Compound.COMP ],
+    { provider }
+  );
+
+  let totalSupply = await Compound.eth.read(
+    cToken,
+    'function totalSupply() returns (uint)',
+    [],
+    { provider }
+  );
+
+  let exchangeRate = await Compound.eth.read(
+    cToken,
+    'function exchangeRateCurrent() returns (uint)',
+    [],
+    { provider }
+  );
+
+  exchangeRate = +exchangeRate.toString() / ethMantissa; 
+  compSpeed = compSpeed / 1e18; // COMP has 18 decimal places
+  compPrice = compPrice / 1e6;  // price feed is USD price with 6 decimal places
+  totalSupply = (+totalSupply.toString() * exchangeRate) / (Math.pow(10, underlyingDecimals));
+  const compPerDay = compSpeed * blocksPerDay;
+
+  return 100 * (compPrice * compPerDay / totalSupply) * 365;
+}
+
+async function calculateApy(cToken, ticker) {
+  const underlyingDecimals = Compound.decimals[cToken.slice(1, 10)];
+  const cTokenAddress = Compound.util.getAddress(cToken);
+  const [supplyApy, compApy] = await Promise.all([
+    calculateSupplyApy(cTokenAddress, ticker),
+    calculateCompApy(cTokenAddress, ticker, underlyingDecimals)
+  ]);
+  console.log(`Supply APY for ${ticker}: ${supplyApy}%`);
+  console.log(`COMP APY for ${ticker}: ${compApy}%`);
+  console.log(`Total APY for ${ticker}: ${supplyApy + compApy}%`);
+  console.log('---');
+}
+
+async function main() {
+  await Promise.all([
+    calculateApy(Compound.cDAI, 'DAI'),
+    calculateApy(Compound.cUSDC, 'USDC'),
+    calculateApy(Compound.cUSDT, 'USDT'),
+  ]);
+}
+
+main();

screencast/266-how-to-calculate-apy-defi/apy2.js

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+const axios = require('axios');
+
+async function main() {
+  const results = await axios.get('https://api.compound.finance/api/v2/ctoken');
+  results.data.cToken.forEach(cToken => {
+    const supplyRate = cToken.supply_rate.value * 100;
+    const compRate = +cToken.comp_supply_apy.value; 
+    console.log(`Supply APY for ${cToken.underlying_symbol}: ${supplyRate}%`);
+    console.log(`COMP Supply APY for ${cToken.underlying_symbol}: ${compRate}%`);
+    console.log(`Total Supply APY for ${cToken.underlying_symbol}: ${compRate + supplyRate}`);
+    console.log('---');
+  });
+}
+
+main();