JS.Class - Ruby-like classes for JavaScript

Callbacks and hooks

Ruby defines a couple of hook methods that you can use to detect when a class is subclassed or when a module is mixed in. These hooks are called inherited(), included() and extended().

If a class has a static method called inherited() it will be called whenever you create a subclass of it:

        var ChildDetector = new JS.Class({
          extend: {
            inherited: function(klass) {
              // Do stuff with child class
            }
          }
        });

The hook receives the new child class as an argument. Note that class is a reserved word in JavaScript and should not be used as a variable name. The child class will have all its methods in place when inherited() gets called, so you can use them within your callback function.

In the same vein, if you include() an object that has a method called included, that method will be called. You can use this to build modules with complex behaviour inside a closure so they cannot be modified from outside:

        var ActiveRecord = (function(){
          var INSTANCE_METHODS = {
            save: function() {},
            validate: function() {},
            attributes: function() {}
          };
        
          var STATIC_METHODS = {
            find: function() {},
            create: function() {}
          };
        
          return {
            included: function(klass) {
              klass.include(INSTANCE_METHODS);
              klass.extend(STATIC_METHODS);
            }
          };
        })();

ActiveRecord is now an object with one public method, included, that tells it what to do when it is mixed into a class. The module is secure as no code outside the module can modify its contents. JS.Class actually includes its own module functionality to do precisely this – see Modules.

The extended() hook works in much the same way as included(), except that it will be called when the object is used to extend() a class.

JS.Class Ruby-like classes for JavaScript

Callbacks and hooks