Here is the code that I am testing
define ( ['N/record', 'N/ui/serverWidget'] ,
// Add the callback function.
function(record, serverWidget) {
function myBeforeLoad (context) {
if (context.type !== context.UserEventType.CREATE && context.type !== context.UserEventType.EDIT)
return;
var form = context.form;
var subrec = objRecord.getCurrentSublistSubrecord({ sublistId: 'item', fieldId: 'inventorydetail' });
var binField = subrec.getSublist({id: 'inventoryassignment'}).getField({id: 'binnumber'});
binField.isMandatory = true;
}
return {
beforeLoad: myBeforeLoad,
};
});