Bits of .NET

🗑️ Know When Objects Are Garbage Collected

WeakMap is known. WeakRef and FinalizationRegistry give advanced memory management. Cache cleanup, resource release, memory leak detection.

📝 WeakRef Example

let obj = { data: 'important' };
const weakRef = new WeakRef(obj);

// Later, obj might be garbage collected
obj = null;

// Check if still alive
const revived = weakRef.deref();
if (revived) {
  console.log('Object still exists:', revived);
} else {
  console.log('Object was garbage collected');
}

🎯 FinalizationRegistry (Cleanup)

const registry = new FinalizationRegistry((heldValue) => {
  console.log(`Object with ${heldValue} was garbage collected`);
  // Close file handles, release external resources
});

let resource = { id: 1, data: 'expensive' };
registry.register(resource, resource.id);

// Later, when resource is no longer referenced
resource = null;
// GC will call the callback with '1'

// Unregister if still needed
registry.unregister(resource);

💡 Use Cases

• Memory-constrained environments (mobile, embedded)
• Cache with automatic cleanup (weak cache)
• Debugging memory leaks (log when objects die)
• Integration with C++ via WebAssembly (manual memory)