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 .