Public and private variables in js classes

I read some articles about js on cnblogs and take the following notes:

First look at code 1:
Function car (){
Var wheel = 3; // Private variable
This. wheel = 4; // public variable
Alert (wheel );
Alert (this. wheel );
}
Var car1 = new car (); Result: 3 4

Code 2:
Function car (){
Var wheel = 3; // Private variable
This. wheel = 4; // public variable
}
Var car1 = new car ();
Alert (car1.wheel); Result: 4

Var wheel = 3 is a local variable, and this. wheel = 4 is a public variable. To access the private variable in the car, see Code 3:
Function car (){
Var wheel = 3; // Private variable
This. wheel = 4; // public variable
This. getPrivateVal = function (){
Return wheel;
}
}
Var car1 = new car ();
Alert (car1.getPrivateVal (); Result: 3