To resolve packages by name and version, npm talks to a registry website that implements the CommonJS Package Registry specification for reading package info.
npm's package registry implementation supports several write APIs as well, to allow for publishing packages and managing user account information.
The npm public registry is powered by a CouchDB database, of which there is a public mirror at https://skimdb.npmjs.com/registry.
The registry URL used is determined by the scope of the package (see
scope. If no scope is specified, the default registry is used, which is
supplied by the
registry config parameter. See
config for more on managing npm's configuration.
When the default registry is used in a package-lock or shrinkwrap is has the special meaning of "the currently configured registry". If you create a lock file while using the default registry you can switch to another registry and npm will install packages from the new registry, but if you create a lock file while using a custom registry packages will be installed from that registry even after you change to another registry.
When making requests of the registry npm adds two headers with information about your environment:
Npm-Scope– If your project is scoped, this header will contain its scope. In the future npm hopes to build registry features that use this information to allow you to customize your experience for your organization.
Npm-In-CI– Set to "true" if npm believes this install is running in a continuous integration environment, "false" otherwise. This is detected by looking for the following environment variables:
bamboo.buildKey. If you'd like to learn more you may find the original PR interesting. This is used to gather better metrics on how npm is used by humans, versus build farms.
The npm registry does not try to correlate the information in these headers with any authenticated accounts that may be used in the same requests.
"private": true in your
package.json to prevent it from being
published at all, or
to force it to be published only to your internal/private registry.
package.json for more info on what goes in the package.json file.