block-number-example.js

const ethers = require("ethers");

(async function() {
  const address = "0x477b8D5eF7C2C42DB84deB555419cd817c336b6F";
  const provider = ethers.getDefaultProvider();
  const block1 = 8821739;
  const block2 = 8821081;
  let balance1 = ethers.utils.formatEther(await provider.getBalance(address, block1));
  let balance2 = ethers.utils.formatEther(await provider.getBalance(address, block2));
  console.log(`balance for block ${block1}: ${balance1}`);
  console.log(`balance for block ${block2}: ${balance2}`);
})();

// balance for block 8821739: 1600.687191129372744769
// balance for block 8821081: 1571.814645737610244769