npm ERR! code UNABLE_TO_GET_ISSUER_CERT_LOCALLY

A quick solution from the internet search was npm config set strict-ssl false, luckily it worked. But as a part of my work environment, I am restricted to set the strict-ssl flag to false.

Later I found a safe and working solution,

npm config set registry http://registry.npmjs.org/  

this worked perfectly and I got a success message Happy Hacking! by not setting the strict-ssl flag to false.

what may be happening is your company decrypts certain traffic and re-encrypts it with their certificate (which you probably already have in your keychain or trusted root certificates)

if you're using node 7 or later I've found this fix to be compatible with node and node-gyp (for Windows you'll need to do this differently, but you basically just need to add this environment variable):

export NODE_EXTRA_CA_CERTS="absolute_path_to_your_certificates.pem" (in Windows you may need to remove the quotes)

the pem file can have multiple certificates: https://nodejs.org/api/cli.html#cli_node_extra_ca_certs_file

make sure your certificates are in proper pem format (you need real line breaks not literal \n)

I couldn't seem to get it to work with relative paths (. or ~)

This fix basically tells npm and node-gyp to use the check against the regular CAs, but also allow this certificate when it comes across it

Ideally you would be able to use your system's trusted certificates, but unfortunately this is not the case.

Changing the NPM repo URL to HTTP works as a quick-fix, but I wanted to use HTTPS.

In my case, the proxy at my employer (ZScaler) was causing issues (as it acts as a MITM, causing certification verification issues)

I forgot I found a script that helps with this and Git (for cloning GitHub repos via HTTPS had the same issue) and forked it for my use

Basically, it does the following for git:

git config --global http.proxy http://gateway.zscaler.net:80/git config --system http.proxy http://gateway.zscaler.net:80/

and for Node, it adds proxy=http://gateway.zscaler.net:80/ to the end of c:\Users\$USERNAME\npm\.npmrc

That solved the issue for me.