Data Element Works only with return Statement

Hi all,

in Adobe Launch I have defined a data element that should be set with a javascript variable on source page of the website.

When I call on browser console _satellite.getVar('MY VAR') it returns null, even if the javascript variable is defined and populated.

After several tests it seems that I can retrieve my data element value only defining it as a custom code type with a return statement like this:

if(MY JAVASCRIPT VARIABLE)

 return MY JAVASCRIPT VARIABLE;

else

return ""

May someone help me understand why?

Thank you