Question

41

how to access javascript object variables in prototype function

rated 0 times [ 47] [ 6] / answers: 1 / hits: 20507 / 13 Years ago, fri, july 22, 2011, 12:00:00

I have the following javascript

function person() {

  //private Variable

  var fName = null;

  var lName = null;



  // assign value to private variable

  fName = Dave;

  lName = Smith;

};



person.prototype.fullName = function () {

  return this.fName +   + this.lName;

};



var myPerson = new person();

alert(myPerson.fullName());

I am trying to get an understanding of object orientated techniques in javascript. I have a simple person object and added a function to its prototype.

I was expecting the alert to have Dave Smith, however I got underfined underfined. why is that and how do I fix it?

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kendellc

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2 Years ago

answered 13 Years ago anais · Accepted Answer

Unfortunately you can't access a private variable. So either you change it to a public property or you add getter/setter methods.

function person() {



    //private Variable

    var fName = null;

    var lName = null;



    // assign value to private variable

    fName = Dave;

    lName = Smith;



    this.setFName = function(value){ fName = value; };

    this.getFName = function(){ return fName; }

};

see javascript - accessing private member variables from prototype-defined functions

But actually this looks like what you are looking for:
Javascript private member on prototype

from that SO post:

As JavaScript is lexically scoped, you can simulate this on a per-object level by using the constructor function as a closure over your 'private members' and defining your methods in the constructor, but this won't work for methods defined in the constructor's prototype property.

in your case:

var Person = (function() {

    var store = {}, guid = 0;



    function Person () {

        this.__guid = ++guid;

        store[guid] = { 

            fName: Dave,

            lName: Smith

        };

    }



    Person.prototype.fullName = function() {

        var privates = store[this.__guid];

        return privates.fName +   + privates.lName;

    };



    Person.prototype.destroy = function() {

        delete store[this.__guid];

    };



    return Person; 

})();





var myPerson = new Person();



alert(myPerson.fullName());



// in the end, destroy the instance to avoid a memory leak

myPerson.destroy();

Check out the live demo at http://jsfiddle.net/roberkules/xurHU/