Here are the steps, in detail ...
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Install Node.js from nodejs.org/en/download
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Update to the latest version of npm:
$ npm install npm -g -
Make a new folder for the npm global packages
$ mkdir ~/.npm-packages -
Tell npm where to find/store them
$ npm config set prefix ~/.npm-packages
Verify the install
# this should show the versions
node -v
npm -v
# this should show npm and ng with no errors
npm list -g --depth=0
Hope it works for you, it worked for me!