1. Find the npm install path
$ npm get prefix
/usr/local/
/usr/local/
is <prefix>
2. Add npm to PATH
# Command format
$ export PATH=$PATH:<prfix>/bin
# Example
$ export PATH=$PATH:/usr/local/bin
3. Add npm path to ~/.bashrc
# Command format
$ echo "export PATH=$PATH:<prefix>/bin" >> ~/.bashrc
# Example
$ echo "export PATH=$PATH:/usr/local/bin" >> ~/.bashrc
Source: https://superuser.com/a/1081802