This is general solutions for all kind of npm permission issue.

sudo chown -R $USER ~/.npm
sudo chown -R  $USER /usr/bin/npm
sudo chown -R  $USER /usr/lib/node_modules/
chmod -R a+x node_modules

Kill any process using port

USE THIS COMMAND ON YOUR OWN RISK !

sudo kill -9 $(sudo lsof -t -i:4200)

If you want to check that if process running than and than kill the process , use bellow one

if sudo lsof -t -i:4200; then sudo kill -9 $(sudo lsof -t -i:4200); fi

Above command will check that process is running than kill by process id.