Develop Reference

A framework for emulating instance and static variables?

I have one here:
http://jsfiddle.net/s9dLb/2/
What I noticed is that in this framework, all variables are static ( they are on the prototype chain ), and are only "instance" based if you set them in the constructor.
I'm using these terms from CS101 usually taught via Java.
Is there a better way to do this?
By default I set instance variables to a string 'instance' which will be replaced once the constructor is called.
var klass = function (obj, config_module) {
if (config_module === 'constructor') {
var object_public;
if (obj.constructor) {
object_public = obj.constructor;
delete obj.constructor;
}
_.some(obj, function (val, key) {
object_public.prototype[key] = val;
});
return object_public;
}
};
var Test = klass({
// instance, set in constructor
A : 'instance',
// static, not set in constructor
B : 4,
constructor: function (some_var) {
this.A = some_var;
},
get: function () {
return 2;
},
set: function () {
}
}, 'constructor');
var instanceA = new Test('A');
var instanceB = new Test('B');
console.log('Start');
console.log(instanceA.A);
console.log(instanceB.A);

Give MooTools a try. It is as close as it can get without the use of other languages which compile to JavaScript (like CoffeScript or TypeScript).
Here is an example MooTools class:
Foo = new Class({
// instance variable:
name: '',
// construtor:
initialize: function(name) {
this._setName(name);
},
// instance method:
getName: function(){
return this.name;
},
// protected instance method:
_setName: function(name) {
this.name = name;
}.protect()
});
// static variable:
Foo.bar = 'bar';
// static method
Foo.bar = function(){}
// instance object:
var myFoo = new Foo('my new name');
var theName = myFoo.getName();
var checkInstance = instanceOf(myFoo, Foo);
Fiddle

Javascript public method parameters as private vars

I am trying to figure out how to have a private instance variable on my class that gets set by a parameter of a public method. In this case, though; it seems that outside of somePublicMethod myPrivateVar will be undefined. How can achieve what I am trying to do ?
MyClass = function() {
var myPrivateVar;
this.somePublicMethod(myPrivateVar) {
myPrivateVar = myPrivateVar //????
}
this.someOtherPublicMethod() {
somePrivateMethod();
}
function somePrivateMethod() {
myPrivateVar++;
}
}

The issue is you're shadowing the var myPrivateVar by giving the argument the same name, so only the argument variable is in scope:
this.somePublicMethod = function(myPrivateVar) {
myPrivateVar = myPrivateVar; // sets the argument to itself
}
You'll need to give one of them a different name to avoid shadowing:
this.somePublicMethod = function(inputVar) {
myPrivateVar = inputVar;
};
Otherwise, you'll need to contain one of them somehow:
MyClass = function () {
var locals = {
myPrivateVar: null
};
this.somePublicMethod = function (myPrivateVar) {
locals.myPrivateVar = myPrivateVar;
};
function somePrivateMethod() {
locals.myPrivateVar++;
}
};

Use this.myPrivateVar:
this.somePublicMethod = function(myPrivateVar) {
this.myPrivateVar = myPrivateVar;
}
To call the private method within the context of this, you can use:
this.somePublicMethod = function(myPrivateVar) {
this.myPrivateVar = myPrivateVar;
somePrivateMethod.call(this); // pass this as the context of the private method
}
function somePrivateMethod() {
this.myPrivateVar++;
}

Have you considered taking a slightly different route?
var MyClass = function(){
var bar = "private";
return {
setBar: function( newBar ) { bar = newBar; },
getBar: function() { return bar; }
}
};
When you new-up an instance of this class, the bar property will be private. However, it will still be accessible by the public setBar and getBar methods.
var inst = new MyClass;
console.log( inst.bar ); // undefined
console.log( inst.getBar() ); // 'private'
inst.setBar( 'accessible' );
console.log( inst.getBar() ); // 'accessible'

Override privileged method of base class

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 accomplish in the simple code example below?
I cannot convert the baseclass function parseXML() to public because it requires access to private variables
function BaseClass()
{
var map = {};
// I cannot make this function public BECAUSE it accesses & changes private variables
this.parseXML = function( key, value )
{
alert("BaseClass::parseXML()");
map[key] = value;
}
}
function ChildClass()
{
BaseClass.call(this);
this.parseXML = function( key, value, otherData )
{
alert("ChildClass()::parseXML()");
// How can I call the base class function parseXML()?
//this.parseXML(); // calls this function not the parent function
//MyClass.prototype.doStuff.call
BaseClass.prototype.parseXML.call(this, key, value); // fails
//BaseClass.prototype.parseXML(); // fails
// perform specialised actions here with otherData
}
}
ChildClass.prototype = new BaseClass;
var a = new ChildClass();
a.parseXML();

function BaseClass() {
var map = {};
this.parseXML = function(key, value) {
alert("BaseClass::parseXML()");
map[key] = value;
}
}
function ChildClass() {
BaseClass.call(this);
var parseXML = this.parseXML;
this.parseXML = function(key, value, otherData) {
alert("ChildClass()::parseXML()");
parseXML.call(this, key, value);
}
}
ChildClass.prototype = new BaseClass;
var a = new ChildClass();
a.parseXML();
Live Example
Basically you cache the privileged method (which is only defined on the object) and then call it inside the new function you assign to the privileged method name.
However a more elegant solution would be:
function BaseClass() {
this._map = {};
};
BaseClass.prototype.parseXML = function(key, value) {
alert("BaseClass::parseXML()");
this._map[key] = value;
}
function ChildClass() {
BaseClass.call(this);
}
ChildClass.prototype = Object.create(BaseClass.prototype);
ChildClass.prototype.parseXML = function(key, value, otherData) {
alert("ChildClass()::parseXML()");
BaseClass.prototype.parseXML.call(this, key, value);
}
var a = new ChildClass();
a.parseXML();
Live Example
Also bonus implementation using pd

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.

JavaScript Binding Objects

How could I do this?
Class
var Factory = (function() {
var Class = function() {
this.name = 'John';
this.methods = {
get: function(callback) {
callback();
}
};
};
return {
createClass: function() {
return new Class();
}
};
}());
Usage
var MyClass = Factory.createClass();
MyClass.methods.get(function() {
this.name // => returns undenfined
});
Thanks for any help!

You need to save a reference to this in the outer Class function and call call:
var instance = this;
this.methods = {
get: function(callback) {
callback.call(instance);
}
};

var Class = function() {
// Save a reference to this that can be used in local closures.
var me = this;
this.name = 'John';
this.methods = {
get: function(callback) {
// Use 'call()', passing the reference to the 'Class' object
callback.call(me);
}
};
};

#SLaks - The declaration of scope as a Global variable is bad practice.
#Ferdinand Beyer - have you tested if it functions?
The better way will be the scope binding. The Prototype javascript framework produced a nice concept and we can easily implement it like
Function.prototype.bind = function(scope) {
var _function = this;
return function() {
return _function.apply(scope, arguments);
}
}
and then yoou code should have only a single change and it will maintin the scope of your class.
var Factory = (function() {
var Class = function() {
this.name = 'John';
var me = this;
this.methods = {
get: function(callback) {
callback();
}
};
};
return {
createClass: function() {
return new Class();
}
};
}());
var MyClass = Factory.createClass();
MyClass.methods.get(function() {
console.info(this.name) // => returns undenfined
}.bind(MyClass));
I mean only the function call get with .bind(MyClass)

Javascript: best Singleton pattern [duplicate]

This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Simplest/Cleanest way to implement singleton in JavaScript?
I'm using this pattern for singletons, in the example the singleton is PlanetEarth:
var NAMESPACE = function () {
var privateFunction1 = function () {
privateFunction2();
};
var privateFunction2 = function () {
alert('I\'m private!');
};
var Constructors = {};
Constructors.PlanetEarth = function () {
privateFunction1();
privateFunction2();
};
Constructors.PlanetEarth.prototype = {
someMethod: function () {
if (console && console.log) {
console.log('some method');
}
}
};
Constructors.Person = function (name, address) {
this.name = name;
this.address = address;
};
Constructors.Person.prototype = {
walk: function () {
alert('STOMP!');
}
};
return {
Person: Constructors.Person, // there can be many
PlanetEarth: new Constructors.PlanetEarth() // there can only be one!
};
}();
Since PlanetEarth's constructor remains private, there can only be one.
Now, something tells me that this self-cooked thing isn't the best one can do, mostly because I don't have an academic education and I tend to solve problems in stupid ways. What would you propose as a better alternative my method, where better is defined as stylistically better and/or more powerful?

(1) UPDATE 2019: ES7 Version
class Singleton {
static instance;
constructor() {
if (instance) {
return instance;
}
this.instance = this;
}
foo() {
// ...
}
}
console.log(new Singleton() === new Singleton());
(2) ES6 Version
class Singleton {
constructor() {
const instance = this.constructor.instance;
if (instance) {
return instance;
}
this.constructor.instance = this;
}
foo() {
// ...
}
}
console.log(new Singleton() === new Singleton());
Best solution found:
http://code.google.com/p/jslibs/wiki/JavascriptTips#Singleton_pattern
function MySingletonClass () {
if (arguments.callee._singletonInstance) {
return arguments.callee._singletonInstance;
}
arguments.callee._singletonInstance = this;
this.Foo = function () {
// ...
};
}
var a = new MySingletonClass();
var b = MySingletonClass();
console.log( a === b ); // prints: true
For those who want the strict version:
(function (global) {
"use strict";
var MySingletonClass = function () {
if (MySingletonClass.prototype._singletonInstance) {
return MySingletonClass.prototype._singletonInstance;
}
MySingletonClass.prototype._singletonInstance = this;
this.Foo = function() {
// ...
};
};
var a = new MySingletonClass();
var b = MySingletonClass();
global.result = a === b;
} (window));
console.log(result);

Why use a constructor and prototyping for a single object?
The above is equivalent to:
var earth= {
someMethod: function () {
if (console && console.log)
console.log('some method');
}
};
privateFunction1();
privateFunction2();
return {
Person: Constructors.Person,
PlanetEarth: earth
};

Extending the above post by Tom, if you need a class type declaration and access the singleton instance using a variable, the code below might be of help. I like this notation as the code is little self guiding.
function SingletonClass(){
if ( arguments.callee.instance )
return arguments.callee.instance;
arguments.callee.instance = this;
}
SingletonClass.getInstance = function() {
var singletonClass = new SingletonClass();
return singletonClass;
};
To access the singleton, you would
var singleTon = SingletonClass.getInstance();