how to unpack after npm pack?

You can call the following command to unzip the package: tar -xzf YOUR_NPM_PACKAGE.tgz.

It's going to produce a folder called package in the directory you called the command.

This can be done with npm install tgz_file.tgz --production command.

It will install that package, along with all of its dependencies, in the path relative to where the command was ran from.