function getPair(
    address tokenA,
    address tokenB
) external view returns (address pair);

function allPairs(uint256 index) external view returns (address pair);
function allPairsLength() external view returns (uint256);

[
  "function getPair(address tokenA, address tokenB) view returns (address pair)",
  "function allPairs(uint256 index) view returns (address pair)",
  "function allPairsLength() view returns (uint256)"
]

function getReserves() external view returns (
    uint112 reserve0,
    uint112 reserve1,
    uint32 blockTimestampLast
);

function token0() external view returns (address);
function token1() external view returns (address);

function totalSupply() external view returns (uint256);
function balanceOf(address owner) external view returns (uint256);

[
  "function getReserves() view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast)",
  "function token0() view returns (address)",
  "function token1() view returns (address)",
  "function totalSupply() view returns (uint256)",
  "function balanceOf(address owner) view returns (uint256)",
  "function approve(address spender, uint256 value) returns (bool)",
  "function transfer(address to, uint256 value) returns (bool)"
]

const FACTORY_ABI = [
  "function getPair(address, address) view returns (address)"
];
const PAIR_ABI = [
  "function getReserves() view returns (uint112, uint112, uint32)",
  "function token0() view returns (address)",
  "function token1() view returns (address)",
  "function totalSupply() view returns (uint256)"
];

const factory = new ethers.Contract(V2_FACTORY, FACTORY_ABI, provider);
const pairAddress = await factory.getPair(tokenA, tokenB);

if (pairAddress === ethers.ZeroAddress) {
  console.log("Pool does not exist");
} else {
  const pair = new ethers.Contract(pairAddress, PAIR_ABI, provider);
  const [reserve0, reserve1] = await pair.getReserves();
  const token0 = await pair.token0();

  console.log(`Reserve ${token0 === tokenA ? 'A' : 'B'}: ${reserve0}`);
  console.log(`Reserve ${token0 === tokenA ? 'B' : 'A'}: ${reserve1}`);
}