This piece of code is to run commands in powershell as administrator.

npmsetup.ps1

Set-ExecutionPolicy Unrestricted -Scope CurrentUser -Force

# Get the ID and security principal of the current user account
$myWindowsID = [System.Security.Principal.WindowsIdentity]::GetCurrent();
$myWindowsPrincipal = New-Object System.Security.Principal.WindowsPrincipal($myWindowsID);

# Get the security principal for the administrator role
$adminRole = [System.Security.Principal.WindowsBuiltInRole]::Administrator;

# Check to see if we are currently running as an administrator
if ($myWindowsPrincipal.IsInRole($adminRole))
{
    # We are running as an administrator, so change the title and background colour to indicate this
    $Host.UI.RawUI.WindowTitle = $myInvocation.MyCommand.Definition + "(Elevated)";
    $Host.UI.RawUI.BackgroundColor = "DarkBlue";
    Clear-Host;
}
else {
    # We are not running as an administrator, so relaunch as administrator

    # Create a new process object that starts PowerShell
    $newProcess = New-Object System.Diagnostics.ProcessStartInfo "PowerShell";

    # Specify the current script path and name as a parameter with added scope and support for scripts with spaces in it's path
    $newProcess.Arguments = "& '" + $script:MyInvocation.MyCommand.Path + "'"

    # Indicate that the process should be elevated
    $newProcess.Verb = "runas";

    # Start the new process
    [System.Diagnostics.Process]::Start($newProcess);

    # Exit from the current, unelevated, process
    Exit;
}

# You can replace below lines with your code 
# npm install -g npm-windows-upgrade
# npm-windows-upgrade -p -v latest
# npm install -g node-gyp@latest
# npm config set msvs_version 2015 –global
# npm install --global windows-build-tools

Write-Host -NoNewLine "Press any key to continue...";
$null = $Host.UI.RawUI.ReadKey("NoEcho,IncludeKeyDown");

Code from msdn blog. This may not execute some command that needs Execution policy Unrestricted. Hence adding that line in the beginning!

Nice one. Useful that it leaves the shell open so one can see eventual error messages