'npm' is not recognized as internal or external command, operable program or batch file

 Add environment variable 

C:\Program Files\nodejs\

To the end of your Path variable on the "User variable" section of the Environment Variables on the System Properties.
After that, reopen your command prompt and type (run cmd as admin.)
         npm

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..."


Refer: https://stackoverflow.com/questions/20992723/npm-is-not-recognized-as-internal-or-external-command-operable-program-or-bat