Public variables and private variables in js classes_javascript skills

I read some articles about js on cnblogs and took notes:

Look at code 1 first:
function car(){
var wheel = 3;//private variable
this .wheel = 4;//Public variable
alert(wheel);
alert(this.wheel);
}
var car1 = new car(); The result is: 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, this.wheel=4 is a public variable. If you want to access the private variables in car, please Look at 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