N/record Module
Field.isMandatory
Property Description: Returns true if the standard or custom field is mandatory on the record form, or false otherwise.
Type: boolean
Supported Script Types: Client and server-side scripts For more information, see SuiteScript 2.0 Script Types.
Module: N/record Module
Sibling Object Members: Field Object Members
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=Field.isMandatory

// Code Example 1

// Add additional code.

//...

var objRecord = record.load({

   type: record.Type.SALES_ORDER,

   id: 275

});



var objSublist = objRecord.getSublist({

   sublistId: 'item'

});



var objField = objSublist.getField({

   fieldId: 'item'

});



if(objField.isMandatory){

   var options = {

      title:'Incomplete Field:',

      message: 'Please complete this field.'

   };

   dialog.alert(options);

//...

// Add additional code.



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_4435755588.html