Node.js Interview Question #113

Question :

How do WeakRef and FinalizationRegistry differ from normal JavaScript references, and when might they be useful in a Node.js application?

Detailed Solution:

1. Normal JavaScript References

A normal reference is a strong reference.

let user = {
  name: "Rahul",
};

let anotherReference = user;
user = null;

The object is still reachable through anotherReference.

Conceptually:

user ───────► Object
               ▲
               │
anotherReference

Because at least one strong reference exists, the garbage collector cannot remove the object.

If both references disappear:

user = null;
anotherReference = null;

then the object may eventually become eligible for garbage collection.

2. What is WeakRef?

WeakRef provides a weak reference to an object.

Unlike a normal reference, a WeakRef does not keep the object alive.

Example:

let user = {
  name: "Rahul",
};

const weakUser = new WeakRef(user);
console.log(weakUser.deref());

deref() gives you the object if it is still alive.

You might get:

{ name: "Rahul" }

However, if the object becomes unreachable elsewhere:

user = null;

the garbage collector is free to remove it.

After garbage collection:

console.log(weakUser.deref());

may return:

undefined

The important point is that .