_javascript technique of public variable and private variable in JS class

On the cnblogs to read some of the articles on JS, make a note:

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 (); The result: 3 4

Code 2:
function car () {
var wheel = 3;//Private variable
This.wheel = 4;//public variable
}
var car1 = new car ();
alert (Car1.wheel); Results: 4

var wheel = 3 is a local variable, this.wheel=4 is a public variable, and if you want to access the private variable in 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 ()); Results: 3