const companies = [
  { name: 'TechCorp', founded: 2010 },
  { name: 'DataSystems', founded: 2015 },
  { name: 'WebSolutions', founded: 2008 }
];

const activeClients = new WeakSet();

activeClients.add(companies[0]);
activeClients.add(companies[2]);

companies.pop();

const result = [
  activeClients.has(companies[0]),
  activeClients.has(companies[1]),
  typeof activeClients.size
];

console.log(result);