What is the correct way to get a response from the main process?

Question

JavaScript

There is a master process that runs fork() (child processes).
They communicate by the method for the main:

example1.on('message', function(worker) {
// Сообщения которые приходят от дочернего
});

process.on('message', function(master) {
// Сообщения которые приходят от главного процесса - дочернему
});

The task is that the child sends data to the main.
process.send('send_itemsCounters');
The master catches this data (and sends its data to the child):

if(worker == 'send_itemsCounters'){
   example1.send({itemsCounters:itemsCounters,sss:1}); 
}

And the child has a certain function that should run only when the answer comes from the main one.
How to implement it?