As an npm user with a paid user account, you can add another npm user with a paid account as a collaborator on a private package you own.
Note: The user you want to add as a collaborator on your private package must have a paid user account. To sign up for a paid account, they can visit https://www.npmjs.com/settings/username/billing, replacing username with their npm username.
When you add a member to your package, they are sent an email inviting them to the package. The new member has to accept the invitation gain access to the package.
Granting access to a private user package on the web
On the npm website, go to the package to which you want to add a collaborator: https://www.npmjs.com/package/<your-package-name>
On the package page, under "Collaborators", click +.
Enter the npm username of the collaborator.
Click Submit.
Granting private package access from the command line interface
To add a collaborator to a package on the command line, run the following command, replacing <user> with the npm username of your collaborator, and <your-package-name> with the name of the private package:
npm owner add <user> <your-package-name>
Granting access to private organization packages
To grant an npm user access to private organization packages, you must have an organization owner add them to your organization, then add them to a team that has access to the private package. For more information, see "Adding members to your organization".