F:\webrowser>npm install -g react-native-cli
npm ERR! code UNABLE_TO_VERIFY_LEAF_SIGNATURE
npm ERR! errno UNABLE_TO_VERIFY_LEAF_SIGNATURE
npm ERR! request to https://registry.npmjs.org/react-native-cli failed, reason:
unable to verify the first certificate

npm ERR! A complete log of this run can be found in:
npm ERR! C:\Users\Administrator\AppData\Roaming\npm-cache_logs\2018-01-11T1
6_55_54_266Z-debug.log

solution

npm config set strict-ssl false

F:\webrowser>npm install -g react-native-cli
C:\Users\Administrator\AppData\Roaming\npm\react-native -> C:\Users\Administrato
r\AppData\Roaming\npm\node_modules\react-native-cli\index.js

• react-native-cli@2.0.1
  added 41 packages in 23.687s