const cache = new WeakMap();

function expensiveOperation(obj) {
  if (cache.has(obj)) {
    console.log('Cache hit!');
    return cache.get(obj);
  }
  
  console.log('Computing result...');
  const result = obj.value * 2;
  cache.set(obj, result);
  return result;
}

const user = { value: 42 };
expensiveOperation(user);
expensiveOperation(user);
expensiveOperation({ value: 42 });