How to retrieve token contract address from uniswap pair

[CryptDevExplorer]

Hi,

i am searching for a way to get an ETH token address from an available UniSwap v2 Token <-> WETH pair.
I found information about getting the pair address when the token address is available, but I am searching exactly the other direction.
So i 've got the address of the pair and just want the address of the token.

I am working with node js and ether js.

Thanks in advance for any helpful information