getSwapAmountsOut

function getSwapAmountsOut(
    uint _amountIn, 
    address[] memory _path
) public view virtual returns (uint[] memory amounts)

//수수료 사용 유무에 따라 swapFee 지정(30 = 0.03%)
uint amountInWithFee = amountIn*(10000-swapFee)
uint numerator = amountInWithFee*(reserveOut);
uint denominator = (reserveIn*10000)+amountInWithFee;        
amountOut = numerator / denominator;

// swap 토큰 개수 얻기
await routerContract.getSwapAmountsOut(
    10000
    [mockToken0Contract.address, mockToken1Contract.address]
)

// 결과
[ BigNumber { value: "10000" }, BigNumber { value: "4984" } ]