1:  const activeUsers = new WeakSet();

   2:  function addUser(user) {

   3:      activeUsers.add(user);

   4:      console.log(`User ${user.name} added`); // Example log message

   5:  }

   6:  function removeUser(user) {

   7:      activeUsers.delete(user);

   8:      console.log(`User ${user.name} removed`); // Example log message

   9:  }

  10:  function processActiveUsers(users) {

  11:      users.forEach(user => {

  12:          if (activeUsers.has(user)) {

  13:              console.log(`User ${user.name} is currently active.`); // perform some operation with active user.

  14:          } else {

  15:              console.log(`User ${user.name} is not currently active.`); // perform another operation if user isn't active

  16:          }

  17:      });

  18:  }

  19:  const user1 = { name: 'Bob' };

  20:  addUser(user1);

  21:  processActiveUsers([user1]); // Bob is active

  22:  removeUser(user1);

  23:  processActiveUsers([user1]); // Bob isn't active