如何在JavaScript中封装

Question

can you please tell me how to do encapsulation in javascript .I have a class Name Car .I want to extend this class with B class .Secondly I want to override and overload the methods in java script.

Here is my fiddle http://jsfiddle.net/naveennsit/fJGrA/

   //Define the Car class
function Car() { }
Car.prototype.speed= 'Car Speed';
Car.prototype.setSpeed = function(speed) {
    this.speed = speed;
    alert("Car speed changed");
}


//Define the Ferrari class
function Ferrari() { }
Ferrari.prototype = new Car();


// correct the constructor pointer because it points to Car
Ferrari.prototype.constructor = Ferrari;

// replace the setSpeed method
Ferrari.prototype.setSpeed = function(speed) {
    this.speed = speed;
    alert("Ferrari speed changed");
}

var car = new Ferrari();
car.setSpeed();

can you explain these two lines

Ferrari.prototype = new Car(); This line show Ferrari is extend by car ?

 Ferrari.prototype.constructor = Ferrari;

what is the used of this line ?

Answer 1

JS, by design does not provide a built-in way to manage the visibility of members of an object. but its flexible enough to allow us to do encapsulation.

Effective write up i found for you is http://www.codeproject.com/Articles/108786/Encapsulation-in-JavaScript

Answer 2

Ferrari.prototype = new Car()

This method adds Car poperties to the Ferrari's prototype. Whatever is returned by the Car(), is added to the existing Ferrari's prototype.

Ferrari.prototype.constructor = Ferrari

Prototype has a constructor property which is overriden by this call Ferrari.prototype = new Car() . This is manually resetting it again.

prototype and constructor object properties

I have edited your fiddle. http://jsfiddle.net/fJGrA/3/

Using closure in javascript you can hide elements within an object or function.

function foo(args){
//this is a private variable.
 var _name = ""

 return{
  getname:function(){
   return _name
   }
  }

 }

 bar = new foo()

 // name can only be accessed from inside the foo function.

Whenever a variable is created with a var keyword within a function, it is accessible only in the scope of that function. Effectively, being private to it.