Creating classed in JavaScript

Posted by Renso on Geeks with Blogs See other posts from Geeks with Blogs or by Renso
Published on Mon, 01 Oct 2012 10:40:41 GMT Indexed on 2012/10/01 21:39 UTC
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Goal:

Creating class instances in JavaScript is not available since you define "classes" in js with object literals. In order to create classical classes like you would in c#, ruby, java, etc, with inheritance and instances.

Rather than typical class definitions using object literals, js has a constructor function and the NEW operator that will allow you to new-up a class and optionally provide initial properties to initialize the new object with.

The new operator changes the function's context and behavior of the return statement.

var Person = function(name) {

   this.name = name;

};   

//Init the person

var dude= new Person("renso");

//Validate the instance

assert(dude instanceof Person);

When a constructor function is called with the new keyword, the context changes from global window to a new and empty context specific to the instance; "this" will refer in this case to the "dude" context.

Here is class pattern that you will need to define your own CLASS emulation library:

var Class = function() {

   var _class = function() {

      this.init.apply(this, arguments);

   };

   _class.prototype.init = function(){};

   return _class;

}

var Person a new Class();

Person.prototype.init = function() {

};

var person = new Person;

In order for the class emulator to support adding functions and properties to static classes as well as object instances of People, change the emulator:

var Class = function() {

   var _class = function() {

      this.init.apply(this, arguments);

   };

   _class.prototype.init = function(){};

   _class.fn = _class.prototype;

   _class.fn.parent = _class;

   //adding class properties

   _class.extend = function(obj) {

      var extended = obj.extended;

      for(var i in obj) {

         _class[i] = obj[i];

      };

      if(extended) extended(_class);

   };

   //adding new instances

   _class.include = function(obj) {

      var included = obj.included;

      for(var i in obj) {

         _class.fn[i] = obj[i];

      };

      if(included) included(_class);

   };

   return _class;

}

Now you can use it to create and extend your own object instances:

//adding static functions to the class Person

var Person = new Class();

Person.extend({

   find: function(name) {/*....*/},   

   delete: function(id) {/*....*/},

});

//calling static function find

var person = Person.find('renso');

   

//adding properties and functions to the class' prototype so that they are available on instances of the class Person

var Person = new Class;

Person.extend({

   save: function(name) {/*....*/},

   delete: function(id) {/*....*/}

});

var dude = new Person;

//calling instance function

dude.save('renso');

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