Override privileged method of base class

Question

How can I go about making a child class override a privileged method of a base class?

If its not possible, is there another way to achieve what I am trying to accomp

Answer 1

IMO, you need to use a Javascript library like Ext Js to simplify this task. Anyway, the following example illustrates how you can write some helper methods. It's a part of an unreleased open source project that I'm working on.

var JWObject = (function () {

    var jwobj = function (){};

    jwobj.prototype = { };

    return jwobj;

})();

var Prototype = (function () {

    var scopeQueue = [ window ];

    return {

        beginScope: function (namespace) {
            var parts = namespace.split('.');
            for (var i = 0; i < parts.length; i++) {
                var name = parts[i],
                    parent = this.getScope(),
                    part = parent[name];

                if (part && !part.__namespace) {
                    throw Error('/* ERROR MESSAGE */');
                }

                scopeQueue.push(parent[name] = (part || { __namespace: true }));
            }
        },

        endScope: function () {
            if (scopeQueue.length > 1) {
                scopeQueue.pop();
            }
        },

        getScope: function () {
            return scopeQueue.pick();
        },

        define: function (name, members) {

            var scope = this.getScope();

            if (scope[name]) {
                throw Error('The prototype already exist.');
            }

            this.extend(members, {
                scope: scope,
                extend: JWObject,
                statics: {}
            });

            // Getting constructor
            var ctor = (members.constructor === Object) ? function() { } : members.constructor;
            delete members.constructor;

            if (typeof members.extend === 'string') {
                members.extend = scope[members.extend];
            }

            if (!members.extend) {
                throw Error('The base class is not specified.');
            }

            // Deriving from parent type
            ctor.prototype = new members.extend();
            members.super = members.extend.prototype;
            delete members.extend;

            members.statics.__class = true;
            this.extend(ctor, members.statics, true);
            delete members.statics;

            // Adding new members
            this.extend(ctor.prototype, members, true);

            // Adding and returning the created prototype
            return scope[name] = ctor;

        },

        extend: function (expando, members, override) {
            for (var m in members) {
                if (override || !expando[m]) {
                    expando[m] = members[m];
                }
            }
        }

    };

})();

Prototype.extend(Array.prototype, {

    pick: function() {
        return this[this.length - 1];
    }

});

Here is the result:

Prototype.beginScope('Sample');

/**
 * Prototype: Sample.Plugin
 */
Prototype.define('Plugin', {

    init: function() {
        alert('init!');
    }

});

Prototype.beginScope('Extension');

/**
 * Prototype: Sample.Extensions.Plugin
 * Extend   : Sample.Plugin
 */
Prototype.define('Foo', {
    extend: Sample.Plugin,

    init: function() {
        this.super.init.call(this);
        alert('child: init!');
    },

    fun: function() {
        this.init();
    },

    statics: {

        create: function() {
            return new Sample.Extension.Foo();
        }

    }

});

Prototype.endScope();
Prototype.endScope();

As you can see in the preceding code, the Prototype object provides some functionality to defining a namespace (Prototype.beginScope, Prototype.endScope and Prototype.getScope) or defining a prototype (Prototype.define).

You can inherit a prototype from another using extend like java.

Prototype.define('Foo', {
    extend: Sample.Plugin,

Or call the base class method as follows:

    init: function() {
        this.super.init.call(this);

Also, every prototype you define with above code will be derived from JWObject by default.