Stuck- Make Object Properties Private

Hello, Can someone kindly help me out here.

For some reason the code is running but i haven’t fully understood about the public properties vs private properties.

This code passed the test but i would appreciate if someone explains to me what is happening.
var Bike = function()

// Only change code below this line.
var gear = 5;

this.getGear = function()
return gear;
this.setGear = function(num)
gear = num;


var myCar = new Car();

var myBike = new Bike();


You can only access or modify gear through the methods. You cannot have myCar.gear = 5; for instance.