Given this code snippet, what will be logged when run on a machine with 4 CPU cores?

Given this code snippet, what will be logged when run on a machine with 4 CPU cores?

const cluster = require('cluster');
const os = require('os');

if (cluster.isPrimary) {
  const numCPUs = os.cpus().length;
  console.log(`Primary process is running`);
  for (let i = 0; i < numCPUs; i++) {
    cluster.fork();
  }
} else {
  console.log(`Worker ${process.pid} started`);
}