Ribbon Button Enable/Disable

Hi Guys,

I need to enable and disable based on custom rule. I have used below code and called from enable  rule. This coding working, but show/hide instead of enable/disable. Please suggest any one.

code :

function customRule()

{

 var GetValue = Xrm.Page.getAttribute("new_custume").getValue();

 if (GetValue == 1) {

 returnfalse;

   }

 else {

 returntrue;

    }

}