To install create-react-app without polluting all your base system with JavaScript files:

$ mkdir www
$ cd www
$ npm init # fill the fields, for almost all of them you can simply hit Enter
$ npm install create-react-app
$ export PATH=$PATH:$(pwd)/node_modules/.bin
$ create-react-app app

Curious thing about the JavaScript ecosystem:

$ ls -l app/node_modules/ | grep -c ^d

Almost 900 packages for a basic web app.