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In an INVOKE script you can define and check for the existence of optional parameters like this:

                     /* Conceptually this script's behavior is controlled by 2 parameters which may or may not be passed to it */
         
     var  Parameter1 = "parameter default value";
              var  Parameter2 = "parameter default value";
         
     /* If either parameter has been passed in the objGlobal object then override the default behavior.    */
              /* Note the destruction of the optional parameters. This is so they do not hang around to interfere   */
              /* with later executions of this script. They are created, passed into the script and then destroyed. */       
        
     if (objGlobal.optParameter1 != null) { Parameter1 = objGlobal.optParameter1; objGlobal.optParameter1 = null; }
        
     if (objGlobal.optParameter2 != null) { Parameter2 = objGlobal.optParameter2; objGlobal.optParameter2 = null; }
          
     /* Now use the values in Parameter1 and Parameter 2 to control how this script behaves */
         
     < etc >   
              < etc >   

As a specific example, imagine an INVOKE script that by default displayed the current customer from the instance list. However, some other scripts reuse it to display a specific customer, which may or may not be in the instance list.

You could handle this situation like this:  

                     /* By default this script displays the current customer from the instance list, so get the customer number */
         
     var RequestedCustomer = objListManager.AKey1[0];
         
     /* If the caller has supplied a specific customer number use it instead (making sure to destroy the optional parameter) */
        
     if (objGlobal.optRequestedCustomer != null)
              {
                 RequestedCustomer              = objGlobal.optRequestedCustomer;
                    objGlobal.optRequestedCustomer = null;
              }
          
     /* Now display the details of the customer identified in RequestedCustomer */

             < etc >   
              < etc >   

In a script that wants to display a specific customer number you could do something like this:

              /* Save the changes and (re)display this customer */
   
          case case KeyEnter:
              {
             var       var CustomerNumber = GETVALUE("CustNo");         /* Get the updated customer number from the current screen */
             SENDKEY       SENDKEY(KeyEnter);                               /* Update the current screen details                       */
                objGlobal.optRequestedCustomer = CustomerNumber; /* Set up the specific customer number you want (re)displayed */   
              NAVIGATE_TO_DESTINATION("uShowCustomerDetails"); /* Redisplay the customer by executing the destination script again */   
           }
           break;