Based on my observation, the book that I am reading about JavaScript states that there's an OOP with JavaScript? It doesn't tell much about it, I mean it wasn't explained how to define a class. Can someone give me a sample snippet?

Thanks

Based on my observation, the book that I am reading about JavaScript states that there's an OOP with JavaScript? It doesn't tell much about it, I mean it wasn't explained how to define a class. Can someone give me a sample snippet?

Thanks

• javascript
• oop

• 3 which book, which code, why, what, accept some answers – ant Commented Feb 8, 2010 at 12:09
• 2 @Andy E: Six not accepted questions within one week is not that bad. – Gumbo Commented Feb 8, 2010 at 12:40
• @Gumbo: Yes, but it starts out as 6 in one week and grows from that. I think it's best to prompt someone to mark some answers as early as possible :-) – Andy E Commented Feb 8, 2010 at 12:56
• @sasori: If any of the answers to your previous questions were satisfactory and/or solved your problem, you may want to mark them "accepted". This is considered good etiquette, and will encourage more users to answer any of your future questions. In any case, welcome to Stack Overflow. – Daniel Vassallo Commented Feb 8, 2010 at 13:00
• @sasori: Please read the FAQ (stackoverflow.com/faq). – Gumbo Commented Feb 8, 2010 at 13:00

7 Answers 7

JavaScript is Prototype based and not class based.

Prototype-based programming is a style of object-oriented programming in which classes are not present, and behavior reuse (known as inheritance in class-based languages) is performed via a process of cloning existing objects that serve as prototypes. This model can also be known as class-less, prototype-oriented or instance-based programming. Delegation is the language feature that supports prototype-based programming.

I recommend this book for a concise, precise explanation of both how to use JS's prototypal inheritance as well as how to emulate classical OO inheritance in JS.

Any function in javascript can be used to create an object:

Example:

function MyPoint(x, y) {
    this.x = x;
    this.y = y;
    this.distanceTo = getDistance;
}

function getDistance(p) {
  var dx = this.x-p.x;
  var dy = this.y-p.y;
  return Math.sqrt(dx*dx + dy*dy);
}

var p0 = new MyPoint(1, 2);
var p1 = new MyPoint(2, 3);

window.alert('The distance is ' + p0.distanceTo(p1));

The following snippet may help you getting started with JavaScript's class-less, instance-based objects:

function getArea() {  
   return (this.radius * this.radius * 3.14);  
}  

function getCircumference() {  
   var diameter = this.radius * 2;  
   var circumference = diameter * 3.14;  
   return circumference;  
}

function Circle(radius) {  
   this.radius = radius;  
   this.getArea = getArea;  
   this.getCircumference = getCircumference;  
}

var bigCircle = new Circle(100);  
var smallCircle = new Circle(2);

alert(bigCircle.getArea());            // displays 31400  
alert(bigCircle.getCircumference());   // displays 618  
alert(smallCircle.getArea());          // displays 12.56  
alert(smallCircle.getCircumference()); // displays 12.56

Example from: SitePoint - JavaScript Object-Oriented Programming

Here are couple different ways

if (typeof FFX == "undefined") {
    FFX = {};
}

//Static class
FFX.Util = ({
     return {
      method:function(){
      }
})();

FFX.Util.method(); 



//Instance class
FFX.Util2 = ({
    // private method
    var methodA=function(){
      alert("Hello");
    };
     return {
      method:function(){
      //Call private method
        methodA();
      }
});
var x= new FFX.Util();
x.method(); 

Another way

function MyClass(){
}

/* privileged functions */
MyClass.prototype.hello = function(){
    alert("Hello");
}   

Also you could see how jquery, prototype and alike handle classes and see if thats fits you needs.

There is no one standard way of doing OOP in JavaScript. Everyone uses slightly different class/instance systems and most books fudge the issue. See this question for discussion of ways to work with OO in JS and pick your favourite.

In JavaScript everything is a object. So even a function is a object. So in js (less then < version 2), function makes classes (which are first class objects themselves). Go here, here and herefor understanding better