What package do you use for creating error responses from Lambda, if any?

What do you mean by 'error responses from lambda'?

I mean to create error responses for 400's and 500's

so API Gateway responses? We don't use a 3rd party library but we have a simple success/fail response builder we reuse across the API GW lambdas

return {“statusCode”: 400, “message”: “that broke”}

but what if you had a Runtime error… undefined is not a function for example lol

our top level lambda has a try/catch - then the caught error just returns similar to what Alex wrote above - and we just log the error in the console so can check what happened

i see

Yeah, we have handleCaughtError and handleUncaughtError functions to deal with 'expected' errors and unexpected ones