Supply ERC20 to Compound with Web3.js

supply-erc20-via-json-rpc.js

// Tell DAI contract to allow 10 DAI to be taken by Compound's contract
daiContract.methods.approve(compoundCDaiContractAddress, web3.utils.toBN(10e18))
.send({
  from: myWalletAddress,
  gasLimit: web3.utils.toHex(150000),     // posted at compound.finance/developers#gas-costs
  gasPrice: web3.utils.toHex(20000000000) // use ethgasstation.info (mainnet only)
}).then((result) => {
  console.log('DAI contract "Approve" operation successful.');
  console.log('Sending DAI to the Compound Protocol...');
  // Mint cDAI by supplying DAI to the Compound Protocol
  const dai = 10e18; // 10 DAI
  return compoundCDaiContract.methods.mint(web3.utils.toBN(dai)).send({
    from: myWalletAddress,
    gasLimit: web3.utils.toHex(600000),
    gasPrice: web3.utils.toHex(20000000000),
  });
}).then((result) => {
  console.log('cDAI "Mint" operation successful.');
  return compoundCDaiContract.methods
    .balanceOfUnderlying(myWalletAddress).call();
}).then((balanceOfUnderlying) => {
  balanceOfUnderlying = web3.utils.fromWei(balanceOfUnderlying).toString();
  console.log("DAI supplied to the Compound Protocol:", balanceOfUnderlying);
  return compoundCDaiContract.methods.balanceOf(myWalletAddress).call();
}).then((cTokenBalance) => {
  cTokenBalance = (cTokenBalance / 1e8).toString();
  console.log("My wallet's cDAI Token Balance:", cTokenBalance);
}).catch((error) => {
  console.error(error);
});