npm install permission denied (macOS)

Question

To install a Bootstrap theme I want to run npm install. However I always receive a permission denied error.

I already tried nvm and then switched with

Answer 1

I entered the following:

cd /Users/Marc/Desktop/Dev
rm -rf ./masterclass/node_mdoules/
chown -R $USER ./masterclass/
cd masterclass    
npm install

once this was completed the results indicated warnings and one notice instead of previous result of no permission and error.

I then entered the following:

% sudo npm install --global firebase-tools

my result was success upon completion of the last terminal entry.