Error: unable to verify the first certificate
Solution
npm config set registry http://registry.npmjs.org/ --global
or
npm config set registry http://registry.npm.taobao.org/ --global
UNABLE_TO_VERIFY_LEAF_SIGNATURE
npm config set strict-ssl false
Also, you can set the proxy for nodejs
npm config set proxy http://proxy.company.com:8080
npm config set https-proxy http://proxy.company.com:8080