A pseudo environment variable named errorlevel stores the exit code:

echo Exit Code is %errorlevel%

Also, the if command has a special syntax:

if errorlevel

See if /? for details.

Example

@echo off
my_nify_exe.exe
if errorlevel 1 (
   echo Failure Reason Given is %errorlevel%
   exit /b %errorlevel%
)

Warning: If you set an environment variable name errorlevel, %errorlevel% will return that value and not the exit code. Use (set errorlevel=) to clear the environment variable, allowing access to the true value of errorlevel via the %errorlevel% environment variable.

If I understand your requirement correctly, I don't think anything is going to be seamless. You require some kind of module to be downloaded onto the client machine that will have access to the their local system resources. Any decent browser is going to throw up horrified warnings to the user.