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V2 Factory & Pair

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V2 Factory

The V2 Factory creates and indexes V2 trading pairs. Each unique token pair has exactly one V2 pool.

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Key Functions

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getPair

Returns the pair contract address for two tokens, or zero address if no pair exists. 
function getPair(
    address tokenA,
    address tokenB
) external view returns (address pair);
Token order does not matter — getPair(A, B) returns the same result as getPair(B, A).

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allPairs

Returns the pair address at a given index. Used for enumeration. 
function allPairs(uint256 index) external view returns (address pair);
function allPairsLength() external view returns (uint256);

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ABI

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

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V2 Pair

Each V2 Pair is an ERC-20 contract (LP token) that also holds the pool reserves and executes swaps.

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Key Functions

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getReserves

Returns the current token reserves and the last block timestamp. 
function getReserves() external view returns (
    uint112 reserve0,
    uint112 reserve1,
    uint32 blockTimestampLast
);
token0 is always the token with the lower address.

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token0 / token1

Returns the addresses of the pool’s tokens. 
function token0() external view returns (address);
function token1() external view returns (address);

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totalSupply / balanceOf

Standard ERC-20 functions for LP token accounting. 
function totalSupply() external view returns (uint256);
function balanceOf(address owner) external view returns (uint256);

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ABI

[
  "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)"
]

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Example: Read Pool State

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}`);
}