Truly private fields in JavaScript

So I was chatting with Christian Blunden about JavaScript, and he asked if it was possible to have private fields in JavaScript.

Now the language doesn’t have a key word but I knew that you could use function scoping to achieve the same affect as I had seen the same thing done using the E programming language.

So after 5 minutes here is what we came up with:

[javascript] function Purse(money) { this.getMoney = function() { return money; } this.setMoney = function(newMoney) { money = newMoney; } } [/javascript]

This will create a truely private field that can only be accessed via the methods.

You can still mix your private getters and setters with prototype methods. eg:

[javascript] Purse.prototype = { add : function( money ) { this.setMoney(this.getMoney() + money); } }

var p = new Purse(2); p.add( 1 ); p.getMoney(); returns 3 [/javascript]

If you tried to access the money field directly it would be undefined.