If you use WScript.Shell's Run function, you can do the following:

var WshShell = new ActiveXObject("WScript.Shell");

WshShell.Run("cmd /c reg add HKLM\ExampleKey", 0, 0);

It may need tweaking, but you can integrate an <INPUT type="text"> tag to provide a means of input for the user to type in a registry key name, or to search, or to add a new DWORD etc.

I agree with the other answer, it provides internal (built-in to Windows API) registry functions, not external commands like reg.exe (an executable file).