I'm trying to API to Walmart, it's working fine for 3P but now I have to do it with 1P. in 1P I need to generate a private key using an OpenSSL. Do we have OpenSSL in Netsuite / JS ? And if we do, can I have a reference ?

I don't know what 3P and 1P are, but if you only need to generate a private key once you can do it with OpenSSL on your computer. Do you need to be generating private keys repeatedly for some reason (and hence dynamically doing so via code)?

Yes each time I connect to Walmart, I have to generate a new key. I see that N/crypto look to be the solution

aye, I was going to suggest N/crypto or cryptojs for general use... often openSSL is used for other thing (such as generating persistent private keys for public key encryption scenarios)