How To Define Class Private Members in JavaScript

gistfile1.js

// Class member encapsulation in JavaScript is very important thing and may be implemented with easy. 
// To define private property or method just use var before the definition or this., 
// if you need to give a public access to property or method. 
// source: http://www.apphp.com/index.php?snippet=javascript-define-class-private-memebrs

<script language="javascript">
FormValidator = function(){
 
    // private data member (property)
    var _digits = "0123456789";
 
    // public data member (property)
    this.digits = "0123456789";
    
    // private data function (method)
    var _isEmpty = function(s){ return((s==null)||(s.length==0))};    
 
    // publick data function (method)
    this.isEmpty = function(s){ return((s==null)||(s.length==0))};        
}
 
/* create a new instance of Validator object */ 
var jsFormValidator = new FormValidator();
 
/* wrong access, errors will be produced */
alert(jsFormValidator._digits);
alert(jsFormValidator._isEmpty());
 
/* valid access */
alert(jsFormValidator.digits);
alert(jsFormValidator.isEmpty());
</script>