Using private members and methods in javascript

Question

var test = function(id, company){
    //public members
    this.id = id;
    this.company = company;
    //private member
    var age = 24;
    //private method
    var getAge = function(){
       return this.age;
    };
    //public method
    this.displayAge = function(){
       console.log(getAge());
    }
}

//invoking 

var t = new test(1, 'XYZ Corp');

t.displayAge(); //undefined

Why is it not getting displayed

What you describe as "private members" are simple *local variables*. You won't be able to access them using `this`. Read http://stackoverflow.com/q/13418669/1048572 — Bergi, Feb 27 '15 at 00:58

score 1 · Answer 1 · answered Feb 27 '15 at 00:49

1

It's not being displayed because this.age is undefined. You want age.

answered Feb 27 '15 at 00:49

Josiah Keller

3,635
3
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errnesto · Answer 2 · 2015-02-27T01:01:35.500

0

Because of the scope of variables in js

A variable is visible inside a function not outside

var a = "foo"
function fooBar () {
  var b = "bar"
  console.log(a) // foo
  console.log(b) // bar
}

console.log(a) // foo
console.log(b) // undefined

edited Feb 27 '15 at 01:01

answered Feb 27 '15 at 00:55

errnesto

822
5
15

score 0 · Answer 3 · answered Feb 27 '15 at 01:04

You want this:

var test = function(id, company){
    //public members
    this.id = id;
    this.company = company;
    //private member
    var age = 24;
    //private method
    this.getAge = function(){
       return age;
    };
    //public method
    this.displayAge = function(){
       console.log(this.getAge());
    }
}

//invoking 

var t = new test(1, 'XYZ Corp');

t.displayAge(); //undefined

Note that both "getAge" and "displayAge" need to be attached to this but your private variable "age" should not be.

Using private members and methods in javascript

3 Answers3