Javascript simulate real private variable and manage it with getter/setter

Question

Do I use correctly simulation of private variable with this way?

var C = function(a) {
    var _private = a + 1;
    // more code...
    Object.defineProperties(this, {
        'privateProp': {
            get: function() {
                return _private;
            },
            set: function(b) {
                _private = b + 2;
            }
        }
    });
}

So with the getter/setter I can manage that private variable. And value of it can be get/set with custom methods.

Let's say this example

var c = new C(5);

console.log(c.privateProp); // 6
c.privateProp = 2;
console.log(c.privateProp); // 4

`privateProp` is a *public* property as you can modify it outside the function. `_private` is a *private* variable. It can also be done using ES6 Symbols too, but I'm not sure exactly what you're asking for — CodingIntrigue, Apr 15 '15 at 08:00

Dan Prince · Accepted Answer · 2016-03-26T19:15:16.577

There is no correct way to simulate private variables, because they are not part of the Javascript specification.

However, there are still a number of ways to simulate them:

With Getters and Setters

This is the same as your answer but with a slightly different syntax:

function Rocket() {
  var _fuel = 100;

  return {
    get fuel() {
      return _fuel;
    }
    set fuel(value) {
      _fuel = value;
    }
  };
}

This syntax allows you to define the getter and setter functions in a more natural way, but comes with the restriction that they must be inside an object literal.

With a Closure

function Rocket() {
  var fuel = 100;

  return {
    getFuel: function() { return fuel; },
    setFuel: function(value) { fuel = value; }
  };
}

This is arguably the most elegant way, because this is how Javascript has worked ever since anonymous functions were added to the specification.

By Convention

function Rocket() {
  this._fuel = 100;

  this.getFuel = function() {
    return this._fuel;
  };

  this.setFuel = function(value) {
    this._fuel = value;
  };
}

The final way is to expose the variable as public, but mark it as private by using an underscore at the beginning of the name.

Javascript simulate real private variable and manage it with getter/setter

1 Answers1

With Getters and Setters

With a Closure

By Convention