npm WARN [email protected] requires a peer of [email protected] - 3 but none is installed

Just do as it says:

npm i [email protected] --save

the option --save is to save this dependency to your project.

I had the same problem and this is the solution:

npm install bootstrap jquery popper.js --save

The system automatically resolves the references for you.

This worked for me -

npm i -g [email protected]