Garbage collection

Reachability

In JavaScript garbage collection is implemented through something called reachability.

Variable that are reachable are kept in memory and not deleted by the garbage collector.

A value is considered to be reachable if it's reachable from a root by a reference or by a chain of references.

However, if an object is not reachable anymore, then it will be deleted by the garbage collector.

Example

let user = {
  name: "John"
};

Let's say we have this global variable user referencing to the object {name: "John"}. If user = null; then the reference to "John" is deleted, thus the object "John" becomes unreachable. It will be garbage collected.

Example

let user = {
  name: "John"
};

let admin = user;

Here, we have two references that points to the "John" object. If user = null; the garbage collector will not delete "John" because it is still reachable via admin.