I am following a tutorial on React using create-react-app. The application is created by create-react-app v1.3.0
create-react-app my-app
T
If you are on linux, check if it works with root access. If it does, stop your server and disable enforcement (for more details, man selinux).
man selinux
sudo setenforce 0
Start your server again (without root), it might work.