If you installed npm on windows and got to this issue
npm : File C:\Program Files\nodejs\npm.ps1 cannot be loaded because running scripts is disabled on this system. For more information, see about_Execution_Policies at https:/go.microsoft.com/fwlink/?LinkID=135170. At line:1 char:1 + npm install -g @angular/cli + ~~~ + CategoryInfo : SecurityError: (:) [], PSSecurityException + FullyQualifiedErrorId : UnauthorizedAccess
One way to resolve this is to open powershell as administrator, then type the following command:
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser