Static variables in JavaScript

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How can I create static variables in
Javascript?

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class="normal">Answer

If you
come from a class-based, statically typed object-oriented language (like Java,
C++ or C#) I assume that you are trying to create a variable or method
associated to a "type" but not to an
instance.

An example using a "classical"
approach, with constructor functions maybe could help you to catch the concepts of basic
OO JavaScript:

function
            MyClass () { // constructor function
 var privateVariable = "foo"; // Private
            variable 

 this.publicVariable = "bar"; // Public variable
            

 this.privilegedMethod = function () { // Public Method

            alert(privateVariable);
 };
}


//
            Instance method will be available to all instances but only load once in memory
            
MyClass.prototype.publicMethod = function () { 

            alert(this.publicVariable);
};

// Static variable shared
            by all instances
MyClass.staticProperty = "baz";

var
            myInstance = new
            MyClass();

staticProperty
is defined in the MyClass object (which is a function) and has nothing to do with its
created instances, JavaScript treats functions as href="http://en.wikipedia.org/wiki/First-class_function" rel="nofollow
noreferrer">first-class objects, so being an object, you can assign
properties to a
function.

UPDATE:
ES6 introduced the ability to href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"
rel="nofollow noreferrer">declare classes through the
class keyword. It is syntax sugar over the existing
prototype-based inheritance.

The href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes/static"
rel="nofollow noreferrer">static keyword allows
you to easily define static properties or methods in a
class.

Let's see the above example implemented
with ES6 classes:

data-hide="false" data-console="true" data-babel="true">

class="snippet-code">

class MyClass {
 // class constructor,
            equivalent to
 // the function body of a constructor
 constructor()
            {
 const privateVariable = 'private value'; // Private variable at the
            constructor scope
 this.publicVariable = 'public value'; // Public
            property

 this.privilegedMethod = function() {
 // Public
            Method with access to the constructor scope variables


            console.log(privateVariable);
 };
 }

 //
            Prototype methods:
 publicMethod() {

            console.log(this.publicVariable);
 }

 // Static
            properties shared by all instances

 static staticProperty = 'static
            value';

 static staticMethod() {

            console.log(this.staticProperty);
 }
}

// We
            can add properties to the class prototype
MyClass.prototype.additionalMethod =
            function() {

            console.log(this.publicVariable);

};

var
            myInstance = new MyClass();
myInstance.publicMethod(); // "public
            value"
myInstance.additionalMethod(); // "public
            value"
myInstance.privilegedMethod(); // "private
            value"
MyClass.staticMethod(); // "static
            value"