JClass

Advanced JavaScript inheritance model providing genuine private members based on John Resig's Inheritance Class

https://npmjs.org/package/jclass

Synopsis

JClass is a lightweight and flexible JavaScript inheritance model providing genuine private members using closures. It's applicable in nodejs and normal web browsers. JClass is implemented using prototype's and brings along multiple features like e.g. propper (and even inheritance consistent)instanceof calls. To come straight to the point:

var Animal = JClass.extend({

    // the constructor method
    init: function(name) {
        // a public value
        this.name = name;
    },

    // a public method
    eat: function() {
        return this.name + ' eats';
    },

    // a private method, indicated by 2 leading underscores
    __behave: function() {
        return this.name + ' behaves';
    }
});

// inherit from 'Animal'
var Cat = Animal.extend({

    init: function(name, color) {
        // call 'init' of the super-class
        this._super(name);
        this.color = color;

        // a private value, indicated by 2 leading underscores
        this.__lives = 9;
    },

    // overwrite 'eat'
    eat: function() {
        var msg = this.__behave();
        // 'this._super' references Animal's 'eat' method
        return msg + ' because ' + this._super() + ' fish';
    },

    // getter for '__lives'
    getLives: function() {
        return this.__lives;
    }
});

var simon = new Cat('simon', 'white');
console.log(simon instanceof Cat);    // true
console.log(simon instanceof JClass); // true

console.log(simon.name);       // 'simon'
console.log(simon.__behave()); // TypeError: Object has no method '__behave'
console.log(simon.eat());      // 'simon behaves because simon eats fish'
console.log(simon.__lives);    // undefined
console.log(simon.getLives()); // 9

This little example shows only the basics. It's even possible to customize and optimize JClass for the various needs of your code by using options (e.g. you can change the naming scheme of private members). Take a look at the examples to get a picture of what is possible and how it's working.

Installation

For node (using npm):

npm install jclass

For web browsers:

<script src="/path/to/jclass.min.js"></script>

Examples

Calling _super methods

var Vehicle = JClass.extend({
    init: function(type) {
        this.type = type;
    },

    drive: function() {
        return 'driving';
    }
});

var Car = Vehicle.extend({
    init: function(color) {
        // call the super 'init'
        this._super('car');
        this.color = color;
    },

    drive: function() {
        // call the super 'drive'
        return this._super() + ' on 4 tires';
    }
});

var myCar = new Car('red');

console.log(myCar.drive()); // 'driving on 4 tires'

Private members and the private object

var Vehicle = JClass.extend({
    init: function(type, price) {
        this.type = type;

        // a private value, indicated by 2 leading underscores
        // because 'privatePattern' is /__.*/ by default
        this.__price = price

        // a private value using the 'private object'
        this.__.consumption = 'too much';
    },

    // a private method
    __drive: function() {
        return 'driving';
    }
});

var Car = Vehicle.extend({
    init: function(color, price) {
        this._super('car', price);
        this.color = color;
    },

    // a getter for 'this.__price'
    getPrice: function() {
        return this.__price;
    },

    forceDrive: function() {
        return this.__drive();
    }
});

var myCar = new Car('red', 10000);

console.log(myCar.__price);        // undefined
console.log(myCar.getPrice());     // 10000
console.log(myCar.__.consumption); // undefined
console.log(myCar.__drive());      // TypeError: Object has no method '__drive'
console.log(myCar.forceDrive());   // 'driving'

Disable tracking

var opts = {
    tracking: false
};

var Vehicle = JClass.extend({
    init: function(type, price) {
        this.type = type;

        // won't be private since there is no tracking
        this.__price = price
        
        // values of the 'private object' stay private though!
        this.__.consumption = 'too much';
    },

    // still a private method since tracking does not affect methods
    // (methods are kown before the first method call)
    __drive: function() {
        return 'driving';
    }
}, opts); // note the second parameter

var Car = Vehicle.extend({
    init: function(color, price) {
        this._super('car', price);
        this.color = color;
    },

    forceDrive: function() {
        return this.__drive();
    }
});

var myCar = new Car('red', 10000);

console.log(myCar.__price);      // 10000
console.log(myCar.__drive());    // TypeError: Object has no method '__drive'
console.log(myCar.forceDrive()); // 'driving'

Final classes using extendable

var opts = {
    extendable: false
};

var Vehicle = JClass.extend({
    init: function(type) {
        this.type = type;

        // a private value
        this.__secret = 'yay!';
    }

}, opts); // note the second parameter

var CarHack = Vehicle.extend({
    init: function() {
        this._super('car');
    },

    // try to get the '__secret'
    getSecret: function() {
        return this.__secret;
    }
});

// 'CarHack' won't be assigned since 'Vehicle' cannot be subclassed anymore

Changing keys

var opts = {
    ctorName      : 'ctor',         // the constructor name
    superName     : '_parent',      // the super method name
    privatePattern: '/^__.+__$/',   // the naming scheme
    privateName   : '_private'      // the name of the private object
};

var Vehicle = JClass.extend({
    ctor: function(type) {
        this.type = type;

        // a private value
        this.__secret__ = 'yay!';

        // a private value using the 'private object'
        this._private.foo = 'bar';
    },

    // a private method
    __drive__: function() {
        return 'driving';
    }
});

var Car = Vehicle.extend({
    ctor: function(color) {
        // call the super 'init'
        this._parent('car');
        this.color = color;
    },

    tellSecrets: function() {
        return this.__drive__() + ' ' + this.__secret__;
    }
});

var myCar = new Car('red');

console.log(myCar.tellSecrets()); // 'driving yay!'

Configuration

Options

The signature of extend is

var SubClass = JClass.extend(properties [, options]);

• properties - (Object, mandatory) - An object that defines the methods of your class. See John Resig's Simple Inheritance technique for more details.

• options - (Object, optional) - An object containing

  • extendable - (Boolean, default: true) - When true, another subclass can inherit from this class. When false, this class cannot be subclassed (e.g. like final classes in Java).

  • ctorName - (String, default: 'init') - The name of the method that is invoked when a new instance of your class is created via new MyClass(). All passed arguments are applied to this method (OO speaking: the constructor's name).

  • superName - (String, default: '_super') - The name of the methods of the super-class. When you call (e.g.) this._super() in your init method, the init method of the super-class is called.

  • enablePrivacy - (String, default: true) - When false, this is equivalent to privatePattern = null plus privateName = null (see below).

  • privatePattern - (RegExp, default: /^__.+/) - A regular expression that defines how your private members look like. /^__.+/ would find __fooFn but not _barFn. Null means that there will be no private members.

  • privateName - (String, default: '__') - In addition to values/methods that match the privatePattern, another private object named privateName is visible in every method's scope. In some cases, you may use this object instead of using tracking (see below). Null means that no additional private object will be used.

  • tracking - (Boolean, default: true) - tracking means that all members of an instance are compared before and after a method call in order to track down any addition or deletion of private values (not methods!). When you call (e.g.) 'this.__foo = 123' inside a method, the key __foo (that also matches the privatePattern) was obviously added and will be detected by the before/after comparison. If your classes have a lot of members, you should use the additional private object defined by privateName to reduce the number of comparisons. Note: when false, all non-methods (even if they match the 'privatePattern') won't be private (this.__foo in our example).

  • methodsKey - (String, default: '_jcMethods_') - The name of the object that holds all private methods during a method call. Note: you only need to change this value in case of a name collision with your code.

  • depthKey - (String, default: '_jcDepth_') - The name of the depth value (0 for JClass, 1 for the first derived class, 2 for the second ...). Note: you only need to change this value in case of a name collision with your code.

  • callerDepthKey - (String, default: '_jcCallerDepth_') - The name of the depth value of the initial caller. Note: you only need to change this value in case of a name collision with your code.

Please note: when extending an existing class, please use identical values for the options ctorName, superName, privatePattern and privateName in order to keep the prototype/inheritence model consistent!

JClass.noConflict()

Use this method when JClass interfers with your code. It returns a reference to the JClass base object and resets the JClass variable to its initial value.

Development

• Source hosted at GitHub
• Report issues, questions, feature requests on GitHub Issues

Authors

Marcel R. (riga)