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For
all those that use Object Oriented Programming know the benefits.
The ability to write reusable code is a real time saver in the long
run. This post will cover how to write the basic structure of
Object Oriented Programming in JavaScript.
The Basics
For those of you that don't know what Object Oriented Programming
(oop) is, it's simply a way of writing code that allows you to reuse
the same code in several other projects. Everything is
encapsulated into nice little packages. This post won't go over
the actual theory of OOP, but I would definitely recommend looking into
it. I'm sure if you Googled it, thousands of entries would come
up.
The Ways
There are a couple of ways to handle creating a class in JavaScript.
- Placing everything inside a function
- Placing everything inside an object
- Using prototype to build a class
Placing Everything Inside a Function
In my opinion this is probably the easiest to read out of all of
them. However it isn't the most efficient from a processor point
of view.
Say were going to build a Dog class.
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| function Dog () {
this.name = "";
this.position = 0;
this.bark = function (){
alert("wuff");
};
this.walk = function(){
this.position += 1;
alert("position = "+this.position);
}
this.getName = function (){
return this.name;
}
}
var dog = new Dog();
dog.name = "Ralph";
dog.bark(); //Popup box with "wuff"
dog.walk(); //Position increases by 1;
alert(dog.getName()); //Outputs dog's name*/ |
Class methods are simply variables assigned to functions, and public
variables simply use "this" infront of their names. If you wish to make
a private variable, you would just create a regular variable
using "var" (e.g. var test = 1;)
Placing Everything Inside an Object
This is handy if you don't want to instantiate the class every time
you want to use it. The downside is that it makes inheritance a
little more difficult.
Here is the same Dog class but using an Object.
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| var Dog = {
name : "",
position: 0,
bark : function(){ alert("wuff") },
walk : function(){
this.position += 1;
alert("position = "+this.position);
},
getName : function(){
return this.name
}
}
Dog.name = "Ralph";
Dog.bark(); //Popup box with "wuff"
Dog.walk(); //Position increases by 1;
alert(Dog.getName()); //Outputs dog's name |
This method uses JavaScript Object Notation (JSON) to layout the
class. Keys go on the left, and values go on the right. Once again
methods are simply functions assigned to variables.
Using prototype to Build a Class
This is probably the preferred method of OOP in JavaScript.
It's a little harder to read, but say if we were to create thousands of
dog objects, this would out perform the other methods. Using
prototypes it doesn't store the functions within the class. This means
you aren't creating thousands of functions, you're only create one
function that is pointed to a thousand times. Plus it's easier to
deal with inheritance.
Here is the Dog class yet again.
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| function Dog (){}
Dog.prototype.name = "";
Dog.prototype.position = 0;
Dog.prototype.bark = function (){
alert("wuff");
}
Dog.prototype.walk = function (){
this.position += 1;
alert("position = "+this.position);
}
Dog.prototype.getName = function(){
return this.name;
}
var dog = new Dog();
dog.name = "Ralph";
dog.bark(); //Popup box with "wuff"
dog.walk(); //Position increases by 1;
alert(dog.getName()); //Outputs dog's name |
What the prototype keyword is doing here is creating a framework. So
when the class is instanciated it will have all the methods and
properties that it needs.
Here is a Puppy class to show how inheritance is done. It
inherits all the methods of the Dog class, but overwrites the bark
method for a more puppy like bark.
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| function Puppy (){}
Puppy.prototype = new Dog();
Puppy.prototype.bark = function (){
alert("Yelp");
}
var puppy = new Puppy();
puppy.name = "Ralph";
puppy.bark(); //Popup box with "Yelp"
puppy.walk(); //Position increases by 1;
alert(puppy.getName()); //Outputs puppy's name |
Conclusion
This is by no means a complete tutorial of everything OOP.
This shows the basic structures of how JavaScript can handle OOP.
Out of the three that were outlined, it is probably best to stick with
the prototype method. If there are any Actionscript 2 people out there,
you'll feel right at home with this method.
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