what is process.env

where can I get the documentation for process.env? what all the variables I can access in that env

what does process.env.port || 1137

I understand process.env is environment and we are looking for port in it. what is || means?

This is a common notation in JavaScript that allows for default values, typically for user provided options, if none are given.

If process.env.port has a value, it is used. If it doesn't have a value, then 1137 will be used.

if process.env.port exist it will use it otherwise it will 1137 . || it is or operator.