customErrorHandler

function customErrorHandler() { 
      console.log("Error : " + error); 
      if (error.instanceof OfficeExtension.Error) { 
         console.log("Debug info : " + JSON.stringify(error.debugInfo) ); 
      } 
}); 

function myFunction () { 
   Excel.run ( function (context) { 
      // some code 

   }.catch( customErrorHandler { 
});