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Error while creating a react-app
There is an open issue with installing global packages using sudo leaving behind files with the wrong ownership. (But people are also having some other problems with create-react-app.)
The short version is run this to fix the ownership, then try create-react-app again:
sudo chown -R $(whoami) ~/.npm
The long version and canonical bug is: Global installs (sudo npm i -g) fail on Mac after 6.5 upgrade. Works fine after 6.4.1 downgrade.