Many npm registry servers require the user of TLS 1.2 (or better) to download packages. Most versions of npm and Node.js support TLS 1.2, but you can test your client by running:
npm install -g https://tls-test.npmjs.com/tls-test-1.0.0.tgz
This will install a test package over an HTTPS connection that already enforces TLS 1.2, instead of going to the public npm registry (which does not yet).
If this command succeeds, it will print the following message:
Hello! The tls-test package was successfully downloaded and installed.
Congratulations! Your package manager appears to support TLS 1.2.
If you do not see this message, then there was a problem downloading the package. You should ensure that you are running a currently supported version of Node.js and install the latest version of npm.
For more information, please see the npm documentation and if you have questions, check out the Software Development board of the GitHub Community forums.