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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

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    which book, which code, why, what, accept some answers Commented Feb 8, 2010 at 12:09
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    @Andy E: Six not accepted questions within one week is not that bad. 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 :-) Commented Feb 8, 2010 at 12:56
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7 Answers 7

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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.

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But you can still emulate aspects of class based inheritance and make it feel like regular classes. js-bits.blogspot.com/2010/08/…
4

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.

JavaScript: The good parts

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2 Comments

Yes. There are also excellent explanations on Douglas Crockford's web site (www.crockford.com).
You might find the videos he's done useful, too - here are a couple. ajaxian.com/archives/… video.yahoo.com/watch/111593/1710507
3

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));
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2

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

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3 Comments

Your example does not use prototype based inheritance at all. This is certainly a valid way to do inheritance, but don't claim that this is prototype based inheritance.
@Keith: Updated my answer: with more accurate terminology... Nevertheless, I think the above can still be considered an example of a prototype-based programming: In prototype-based systems there are two methods of constructing new objects, through cloning of an existing object, and through ex nihilo ("from nothing") object creation. Source: en.wikipedia.org/wiki/…
@DanielVassallo Thank you for this example, makes it easy coming from Java :)
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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.

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2

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.

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1

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

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