We got this error in UCI and not in Legacy WebClient,

1. We were Passing CRM Parameter PrimaryControl to Button in Ribbon workbench

   

2. In JS we were getting FormContext from primaryControl(Executioncontext) which was working fine in the Legacy app
   

   function readXML(primaryControl) {   
   var formContext  = null;
    if (primaryControl!== null) { 
               formContext = primaryControl.getFormContext(); 
            }
       }
   }

3. But when same is called in UCI we get ” ” Script Error, Because here we need to treat primary control as formContext

   

So final change needed in Code is as below

function readXML(primaryControl) {   
var formContext  = null;
 if (primaryControl!== null) {
         if (typeof primaryControl.getAttribute === 'function') {
             formContext = primaryControl; //called from the ribbon.
         } else if (typeof primaryControl.getFormContext === 'function' 
                 && typeof(primaryControl.getFormContext()).getAttribute === 'function') {
            formContext = primaryControl.getFormContext(); // most likely called from the form via a handler
         }
    }
}