JavaScript private methods

Question

To make a JavaScript class with a public method I\'d do something like:

function Restaurant() {}

Restaurant.prototype.buy_food = function(){
   // something         


        

Answer 1

This is what I worked out:

Needs one class of sugar code that you can find here. Also supports protected, inheritance, virtual, static stuff...

;( function class_Restaurant( namespace )
{
    'use strict';

    if( namespace[ "Restaurant" ] ) return    // protect against double inclusions

        namespace.Restaurant = Restaurant
    var Static               = TidBits.OoJs.setupClass( namespace, "Restaurant" )


    // constructor
    //
    function Restaurant()
    {
        this.toilets = 3

        this.Private( private_stuff )

        return this.Public( buy_food, use_restroom )
    }

    function private_stuff(){ console.log( "There are", this.toilets, "toilets available") }

    function buy_food     (){ return "food"        }
    function use_restroom (){ this.private_stuff() }

})( window )


var chinese = new Restaurant

console.log( chinese.buy_food()      );  // output: food
console.log( chinese.use_restroom()  );  // output: There are 3 toilets available
console.log( chinese.toilets         );  // output: undefined
console.log( chinese.private_stuff() );  // output: undefined

// and throws: TypeError: Object #<Restaurant> has no method 'private_stuff'

Answer 2

Personally, I prefer the following pattern for creating classes in JavaScript :

var myClass = (function() {
    // Private class properties go here

    var blueprint = function() {
        // Private instance properties go here
        ...
    };

    blueprint.prototype = { 
        // Public class properties go here
        ...
    };

    return  {
         // Public class properties go here
        create : function() { return new blueprint(); }
        ...
    };
})();

As you can see, it allows you to define both class properties and instance properties, each of which can be public and private.

---

Demo

var Restaurant = function() {
    var totalfoodcount = 0;        // Private class property
    var totalrestroomcount  = 0;   // Private class property
    
    var Restaurant = function(name){
        var foodcount = 0;         // Private instance property
        var restroomcount  = 0;    // Private instance property
        
        this.name = name
        
        this.incrementFoodCount = function() {
            foodcount++;
            totalfoodcount++;
            this.printStatus();
        };
        this.incrementRestroomCount = function() {
            restroomcount++;
            totalrestroomcount++;
            this.printStatus();
        };
        this.getRestroomCount = function() {
            return restroomcount;
        },
        this.getFoodCount = function() {
            return foodcount;
        }
    };
   
    Restaurant.prototype = {
        name : '',
        buy_food : function(){
           this.incrementFoodCount();
        },
        use_restroom : function(){
           this.incrementRestroomCount();
        },
        getTotalRestroomCount : function() {
            return totalrestroomcount;
        },
        getTotalFoodCount : function() {
            return totalfoodcount;
        },
        printStatus : function() {
           document.body.innerHTML
               += '<h3>Buying food at '+this.name+'</h3>'
               + '<ul>' 
               + '<li>Restroom count at ' + this.name + ' : '+ this.getRestroomCount() + '</li>'
               + '<li>Food count at ' + this.name + ' : ' + this.getFoodCount() + '</li>'
               + '<li>Total restroom count : '+ this.getTotalRestroomCount() + '</li>'
               + '<li>Total food count : '+ this.getTotalFoodCount() + '</li>'
               + '</ul>';
        }
    };

    return  { // Singleton public properties
        create : function(name) {
            return new Restaurant(name);
        },
        printStatus : function() {
          document.body.innerHTML
              += '<hr />'
              + '<h3>Overview</h3>'
              + '<ul>' 
              + '<li>Total restroom count : '+ Restaurant.prototype.getTotalRestroomCount() + '</li>'
              + '<li>Total food count : '+ Restaurant.prototype.getTotalFoodCount() + '</li>'
              + '</ul>'
              + '<hr />';
        }
    };
}();

var Wendys = Restaurant.create("Wendy's");
var McDonalds = Restaurant.create("McDonald's");
var KFC = Restaurant.create("KFC");
var BurgerKing = Restaurant.create("Burger King");

Restaurant.printStatus();

Wendys.buy_food();
Wendys.use_restroom();
KFC.use_restroom();
KFC.use_restroom();
Wendys.use_restroom();
McDonalds.buy_food();
BurgerKing.buy_food();

Restaurant.printStatus();

BurgerKing.buy_food();
Wendys.use_restroom();
McDonalds.buy_food();
KFC.buy_food();
Wendys.buy_food();
BurgerKing.buy_food();
McDonalds.buy_food();

Restaurant.printStatus();

See also this Fiddle.

Answer 3

Here is the class which I created to understand what Douglas Crockford's has suggested in his site Private Members in JavaScript

function Employee(id, name) { //Constructor
    //Public member variables
    this.id = id;
    this.name = name;
    //Private member variables
    var fName;
    var lName;
    var that = this;
    //By convention, we create a private variable 'that'. This is used to     
    //make the object available to the private methods. 

    //Private function
    function setFName(pfname) {
        fName = pfname;
        alert('setFName called');
    }
    //Privileged function
    this.setLName = function (plName, pfname) {
        lName = plName;  //Has access to private variables
        setFName(pfname); //Has access to private function
        alert('setLName called ' + this.id); //Has access to member variables
    }
    //Another privileged member has access to both member variables and private variables
    //Note access of this.dataOfBirth created by public member setDateOfBirth
    this.toString = function () {
        return 'toString called ' + this.id + ' ' + this.name + ' ' + fName + ' ' + lName + ' ' + this.dataOfBirth; 
    }
}
//Public function has access to member variable and can create on too but does not have access to private variable
Employee.prototype.setDateOfBirth = function (dob) {
    alert('setDateOfBirth called ' + this.id);
    this.dataOfBirth = dob;   //Creates new public member note this is accessed by toString
    //alert(fName); //Does not have access to private member
}
$(document).ready()
{
    var employee = new Employee(5, 'Shyam'); //Create a new object and initialize it with constructor
    employee.setLName('Bhaskar', 'Ram');  //Call privileged function
    employee.setDateOfBirth('1/1/2000');  //Call public function
    employee.id = 9;                     //Set up member value
    //employee.setFName('Ram');  //can not call Private Privileged method
    alert(employee.toString());  //See the changed object

}

Answer 4

All of this closure will cost you. Make sure you test the speed implications especially in IE. You will find you are better off with a naming convention. There are still a lot of corporate web users out there that are forced to use IE6...

Answer 5

You can do it, but the downside is that it can't be part of the prototype:

function Restaurant() {
    var myPrivateVar;

    var private_stuff = function() {  // Only visible inside Restaurant()
        myPrivateVar = "I can set this here!";
    }

    this.use_restroom = function() {  // use_restroom is visible to all
        private_stuff();
    }

    this.buy_food = function() {   // buy_food is visible to all
        private_stuff();
    }
}

Answer 6

Wrap all code in Anonymous Function: Then , all functions will be private ,ONLY functions attached to window object :

(function(w,nameSpacePrivate){
     w.Person=function(name){
         this.name=name;   
         return this;
     };

     w.Person.prototype.profilePublic=function(){
          return nameSpacePrivate.profile.call(this);
     };  

     nameSpacePrivate.profile=function(){
       return 'My name is '+this.name;
     };

})(window,{});

Use this :

  var abdennour=new Person('Abdennour');
  abdennour.profilePublic();

FIDDLE