google+javascriptbanktwitter@js_bankfacebook@jsbankrss@jsbank
Guest, register






Encapsulation in OOP JavaScript Encapsulation is a very useful technique in Object-Oriented programming which allows you to separate an abstraction's implementation from its interface class, thus enabling future changes to the implementation without affecting the interface. In this free HTML JavaScript tutorial, James Padolsey guides you how to create encapsulation in OOP JavaScript, please go to the detailed post for full instructions and JavaScript example codes.


Label: Object-Oriented programming, OOP JavaScript, HTML JavaScript tutorial, abstraction, implementation, interface

Free iPage Web Hosting for First Year NOW



If you're still looking for a reliable web host provider with affordable rates, why you don't take a little of time to try iPage, only with $1.89/month, included $500+ Free Extra Credits for the payment of 24 months ($45)?

Over 1,000,000+ existisng customers can not be wrong, definitely you're not, too! More important, when you register the web hosting at iPage through our link, we're going to be happy for resending a full refund to you. That's awesome! You should try iPage web hosting for FREE now! And contact us for anything you need to know about iPage.
Try iPage for FREE First Year NOW

Real encapsulation, the hard way

For real encapsulation, the following criteria need to be met:

  • You must be able to define private properties within the constructor and methods.
  • You must be able to access and manipulate the private properties within the constructor and methods.
  • The private properties must not be directly accessible from outside (i.e. as properties on the instance).

To fulfill these criteria we're going to need to create a small abstraction that will enable us to define our constructor, its methods, and its properties in a plain object, which will then be processed to produce the required constructor and prototype.

In accordance with convention, this abstraction will be named Class. This is how it will typically work:

var Person = new Class({

 
    _name: 'Blank',
    _age: 0,
 
    init: function(name, age) {

        this.name = name;
        this.age = age;

    },
 
    toString: function() {
        return 'Name: ' + this.name + ', Age: ' + this.age;

    },
 
    setAge: function(age) {
        this.age = age;

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

    }
 
});

The underscore prefix tells Class that we want those properties to be private. Privacy is achieved by retaining a truly private (in a closure) privates array, each item within the array represents the private properties of each instance. This will be clearer once you've seen the source (below).

Class looks for an init method to use as the constructor.

Here's the source for Class, excluding the function:

function Class(o){
 
    var id = 0,

        privates = {},
        instancePrivates = [],
        constructor = function(){

 
            this.__id = id++;
 
            // Copy privates over to new privates obj,
            // just for this instance.
            instancePrivates[this.__id] = {

                privates: merge({}, privates),
                constructor: this

            };
 
            if (this.init) {
                this.init.apply(this, arguments);

            }
 
            return this;
 
        },
        m;

 
    function method(name, fn) {
 
        constructor.prototype[name] = function() {

 
            var i, ret,
                thisPrivates = instancePrivates[this.__id] || {};

 
            // Check constructor
            if (thisPrivates.constructor !== this) {

                // this.__id has been changed, exit.
                return;
            }
 
            thisPrivates = thisPrivates.privates;

 
            for (i in thisPrivates) {
                this[i] = thisPrivates[i];

            }
 
            ret = fn.apply(this, arguments);

 
            for (i in thisPrivates) {
                thisPrivates[i] = this[i];

                delete this[i];
            }
 
            return ret;

 
        };
 
    };
 
    for (m in o) {

 
        // Test for privates
        if ( /^_/.test(m) ) {

 
            privates[m.replace(/^_/, '')] = o[m];

 
        } else {
 
            method(m, o[m]);

 
        }
 
    }
 
    return constructor;
 
}

There are cleaner ways of implementing this, but just for readability's sake, we're identifying each instance with a simple __id property. Yes, this can be manipulated from the outside, but doing so would result in the methods not running.

It has some constraints, but it does provide us with encapsulation:

var Person = new Class({

 
    _name: 'Blank',
    _age: 0,
 
    init: function(name, age) {

        this.name = name;
        this.age = age;

    },
 
    toString: function() {
        return 'Name: ' + this.name + ', Age: ' + this.age;

    },
 
    setAge: function(age) {
        this.age = age;

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

    }
 
});
 
// Testing:
 
var jimmy = new Person('Jim', 88);

 
jimmy._name; // undefined
jimmy.name; // undefined
 
jimmy.toString(); // => "Name: Jim, Age: 88"

 
jimmy.setName('Jimmy');
jimmy.toString(); // => "Name: Jimmy, Age: 88"

 
jimmy.setAge(54);
jimmy.toString(); // => "Name: Jimmy, Age: 54"

 
jimmy._age; // undefined
jimmy.age; // undefined

You can also have private methods, e.g.

var Box = new Class({
 
    _width: 0,

    _height: 0,
 
    init: function(width, height) {

        this.width = width;
        this.height = height;

    },
 
    info: function() {
        return 'Width: ' + this.width +

                ',\nHeight: ' + this.height +
                ',\nArea: ' + this.calcArea();

    },
 
    _calcArea: function() {
        return this.width * this.height;

    }
 
});
 
var myBox = new Box(100, 100);

 
myBox.calcArea; // undefined
myBox._calcArea; // undefined
 
myBox.info(); // => "Width: 100,\nHeight: 100,\nArea: 10000"

Conclusion

The method I used to achieve full encapsulation, while quite novel, isn't going to be appropriate in all situations. The population and clearing of private variables has to happen on every method call, and so will likely cause a significant overhead in some applications.

That said, I don't think the overhead will be all that significant, unless you've got a crazy amount of private properties/methods.

I hope this post has given you some insight into how you can achieve encapsulation and information-hiding in JavaScript.

iPhoneKer.com
Save up to 630$ when buy new iPhone 15

GateIO.gomymobi.com
Free Airdrops to Claim, Share Up to $150,000 per Project

https://tooly.win
Open tool hub for free to use by any one for every one with hundreds of tools

chatGPTaz.com, chatGPT4.win, chatGPT2.fun, re-chatGPT.com
Talk to ChatGPT by your mother language

Dall-E-OpenAI.com
Generate creative images automatically with AI

AIVideo-App.com
Render creative video automatically with AI

JavaScript by day


Google Safe Browsing McAfee SiteAdvisor Norton SafeWeb Dr.Web