Static variables in a Javascript class

javascript, object, static-members, static-methods

Solution

Yes, that is the correct approach to create private static variables.

However, I would treat the `static_fn` different. It seems you want it to be public.

- It should be on your "class"es prototype as it does not interact with private instance variables

- It even does not interact with instances at all. The usual approach is to put such a function/variable on the "class" itself, i.e. the constructor in JS. As the constructor is a `Function` object, it can be extended with properties as any other js object.

var ObjClass = (function closure(){

    var static_var = 0; //static private (scoped) variable
    function static_fn(){ return static_var; }; //static private (scoped) function

    function ObjClass() {
        var thisNumber = ++static_var; // private instance variable
        this.getThisNumber = function() { // public instance method
            return thisNumber; // "privileged" to access scoped instance variables
        };
    }
    ObjClass.getStaticNumber = static_fn; // make the static_fn public
    return ObjClass;
})();



var obj1 = new ObjClass;
var obj2 = new ObjClass;
console.log(ObjClass.getStaticNumber()); //output `2`
var obj3 = new ObjClass;
console.log(ObjClass.getStaticNumber()); //output `3`

console.log(obj1.getThisNumber()); //output `1`
console.log(obj2.getThisNumber()); //output `2`
console.log(obj3.getThisNumber()); //output `3`

Problem

Original source