Understanding Private properties

1

I completed the challenge, but I don’t understand the purpose of a private property. In the Bike constructor, why can’t I just use the public method:

this.setGear = function (val) {
gear = val;
};

and then, just delete everything else in the constructor?

Your code so far

var Car = function() {
  // this is a private variable
  var speed = 10;

  // these are public methods
  this.accelerate = function(change) {
    speed += change;
  };

  this.decelerate = function() {
    speed -= 5;
  };

  this.getSpeed = function() {
    return speed;
  };
};

var Bike = function() {

  // Only change code below this line.
  var gear = 5;
  
  this.setGear = function (val) {
    gear = val;
  };
  
  this.getGear = function () {
    return gear;
  };
};

var myCar = new Car();

var myBike = new Bike();

myBike.getGear();
myBike.setGear(3);```
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**Link to the challenge:**
https://www.freecodecamp.org/challenges/make-object-properties-private