Instanceof and class details in Javascript

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How does instanceof work in JavaScript?
When JavaScript checks whether an object is an instance of a class, it is often obj. Instanceof Class
For example:
Function Class1 (){};
Function Class2 (){};
Class2.prototype = New Class1 ();
Function Class3 (){};
Class3.prototype = New Class2 ();
Function Class4 (){};
VaR OBJ = New Class3 ();
Alert (OBJ Instanceof Class3 ); // True
Alert (OBJ Instanceof Class2 ); // True
Alert (OBJ Instanceof Class1 ); // True

But have you ever wondered how the interpreter judges whether an object is a class instance? Most of the Internet is determined by the prototype chain.
We may see that class4 is not used, so add this sentence later.
Class2.prototype = New Class4 ();
Alert (OBJ Instanceof Class3 ); // True;
Alert (OBJ Instanceof Class2 ); // False;
Alert (OBJ Instanceof Class1 ); // True ;//

In JavaScript, each function has a prototype attribute, which is used to implement the inheritance mechanism. The function class1 defined below is required:
Function class1 (){}
Class1.prototype = {A: 10, B: 100 };
Each instance of class1 inherits the attributes a and B from prototype.

At the same time, each object will have an internal attribute _ PROTO _ (different JavaScript Virtual Machine implementations may use different names), which is invisible to JS developers, it is only used inside the VM. Every time an object is created, the _ PROTO _ of this object will be assigned the prototype of the constructor of this object, in this way, the _ PROTO _ attribute of the object references the same object as the prototype of the constructor. Once the object is created, the _ PROTO _ attribute will not change. In this way, A _ PROTO _ chain is formed through the _ PROTO _ attribute of the object and the _ PROTO _ attribute of the object referenced by _ PROTO. When accessing the attributes and methods of an object, the JS virtual machine is searched through the _ PROTO _ chain.

About instanceof:
Suppose there is a statement like this:
O instanceof C;
During the preceding statement execution, the virtual opportunity sets C. nodes on the _ PROTO _ chain of prototype and O are compared one by one. If an equal node is found, true is returned; otherwise, false is returned.