How check a "Check Box"?

Hello,

I am trying the next:

If I have the check box selected return the birthday in a textfield.

If I have not the check box selected return "nothing"

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var check = session.findbyid("wnd[0]/usr/boxpersonas_40/chkpersonas_46").selected; // to know if the check box is selected

Go to transaction and get the value // OK

var birth = session......................................

Return to main screen // OK

session.findbyid("wnd[0]/usr/boxpersonas_40/chkpersonas_46").selected = check;  // to activate o desactivate the check box, I think that after press the button the checkbox is always NOT SELECTED.

if (check == "true")

     {

          session.findbyid("wnd[0]/usr/boxpersonas_40/txtpersonas_51").text = birth;

     }

else

     {

          session.findbyid(wnd[0]/usr/boxpersonas_40/txtpersonas_51").text = "Nothing";

     }

Thanks!!!