classkit

How I make classes. Sometimes.

Call Class.extend, passing a callback function that returns a class descriptor, an array whose first element is the class constructor and whose successive values are interpreted as pairs of feature names/parameters.

Simple Usage

var Person = Class.extend(function() {

  return [

    // this is the Person constructor
    function(name) {
      this.name = name;
    },
  
    // instance methods feature + method dictionary
    'methods', {
      greet: function() {
        return "I am " + this.name;
      }
    }
  
  ];

});

// when extending classes, super prototype is passed
// to callback function for capture by closure.
var RudePerson = Person.extend(function(_super) {

  return [

    function(name) {
      _super.constructor.apply(this, arguments);
    },

    'methods', {
      greet: function() {
        return "GET OUT OF MY WAY, " + _super.greet.call(this).toUpperCase();
      }
    }

  ];

});

console.log((new Person('Jason')).greet());
console.log((new RudePerson('Bob')).greet());

Delegation

Using the delegate feature, classes can automatically generate methods that delegate their behaviour to some other class property.

See:

Class.extend(function() {
  return [
    
    function() {
      this.events = new EventEmitter();
    },
    
    'delegate', {
      
      // 'foo.on' forwards to 'foo.events.on'
      'on': 'events',

      // 'foo.emit' forwards to 'foo.events.emit'
      'emit': 'events'

      // 'foo.onceOnly' forwards to 'foo.events.one'
      'onceOnly': ['events', 'one']

    }

  ];
});

Hooks

Hooks can be used to define methods that, when called, will automatically forward to all hooks sharing the same name, all the way down the inheritance tree. Hooks defined in ancestor classes are called first.

A = Class.extend(function() {
  return [

    function() {},

    'hooks', {
      componentWillMount: function() {
        console.log("A::componentWillMount");
      }
    }

  ]
});

B = A.extend(function() {
  return [

    function() {},

    'hooks', {
      componentWillMount: function() {
        console.log("B::componentWillMount");
      }
    }

  ]
});

var b = new B();
b.componentWillMount();
// => A::componentWillMount
//    B::componentWillMount

Adding Features

Subclasses can define new Features. A Feature is simply a function that receives the class constructor and some configuration data as parameters and then effects change on the new class' prototype. Here's an example that auto-generates getters and setters:

var PropertyObject = Class.extend();

function makeProperty(proto, name, value) {
  var suffix = name.charAt(0).toUpperCase() + name.substring(1);

  proto['get' + suffix] = function() { return this[name] || value; };
  proto['set' + suffix] = function(v) { this[name] = v; };
}

// a feature receives the new class' constructor function and
// a parameters object which contains configuration data for
// the feature
PropertyObject.Features.getset = {
  apply: function(ctor, props) {
    for (var k in props) {
      makeProperty(ctor.prototype, k, props[k]);
    }
  }
};

var Person = PropertyObject.extend(function() {
  return [
    function() {},

    // dictionary of properties for Person class
    'getset', {
      name: 'A Nameless One',
      age: '100'
    }
  ];
});

var person = new Person;
console.log(person.getName()); // => "A Nameless One"

person.setName("Jason");
console.log(person.getName()); // => "Jason"