npm : The term 'npm' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the code example

Example: 'npm' is not recognized as an internal or external command, operable program or batch file.

Open the Control Panel (Click the Start button, then click Control Panel)
Click User Accounts
Click Change my environment variables
Select PATH and click the Edit... button
At the end of the Variable value, add ;C:\Program Files\nodejs
Click Ok on the "Edit User Variable" window, then click Ok on the "Environment Variables" window
Start a command prompt window (Start button, then type cmd into the search and hit enter)
At the prompt (C:\>) type npm and hit enter; you should now see some help text (Usage: npm <command> etc.) rather than "npm is not recognized..."
Now you can start using npm!