Answer by koga73 for npm 5 install folder without using symlink

I wrote npm-install-offline which allows you to install npm packages from a local repository or folder. By default it copies the folder on install but you can also choose to symlink.https://www.npmjs.com/package/npm-install-offline

npx npm-install-offline ../some-package

Or

npx npm-install-offline my-npm-package --repo ./my-offline-npm

It also will install the package dependencies which npm does not do with local packages.