Static variables in a Javascript class

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.

1. It should be on your "class"es prototype as it does not interact with private instance variables
2. 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`