Wednesday, January 7, 2009

Object-Oriented JavaScript, how to achieve private properties/fields

The very basic of Object-Oriented Programming (OOP) is private fields and public methods (not considering features like polymorphism, inheritance, etc). So how to achieve this very basic of OOP in JavaScript. It turns out to be easy. Here is how to have private fields in your custom JavaScript functions/classes and using methods of your function/class to amend it.

function User() { 
  var name = ''; 
  return { 
    setName: function(newName) { 
      name = newName; 
    }, 
    getName: function() { 
      return name; 
    } 
  } 
} 
var user = User(); 
user.setName("My Name"); 
user.getName(); // My Name

The User() class we just created could be considered a bean in Java. Using this template you can have as many private fields and public methods as you want.

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2 comments:

  1. Elijah ManorJune 8, 2009 at 7:38 AM

    Hmm, interesting. I've never seen anyone do that before.

    I was plesantly surprised to see...

    var user = User();
    user.setName("My Name");
    user.getName(); //My Name
    user.name = "Your Name";
    user.getName();

    to only show "My Name" and not "Your Name"!

    Thanks for the tip!

    ReplyDelete
  2. AnonymousJune 21, 2009 at 8:28 AM

    Prototype's version -)

    var User = Class.create();

    User.prototype =
    {
    initialize: function()
    {
    // it's our constructor
    },

    setName: function(name)
    {
    this.name=name;
    },

    getName: function()
    {
    return this.name;
    }
    }

    ReplyDelete