Question

I’m trying to create something similar to static languages “static field”. Basically: counter property should be incremented every time the init function is called, but no matter on which instance. This is a sample code I’m using to test ( http://jsfiddle.net/HK8BY/2/ ) :

var Widget = {
    counter: 0,
    init: function () {
        this.counter++;
        console.log("init called: " + this.counter);
    }
};

var t1 = Object.create(Widget);
var t2 = Object.create(Widget);
t1.init(); // should print: init called 1
t2.init(); // should print: init called 2
console.log(t1);
console.log(t2);

Currently when I console.log instanes, I see that both proto and instance contain counter property. I thought that with this approach, only proto will have it.

So how can I change it to have only counter in prototype?

Answer 1

var twitter = (function() {
    var counter = 0;
    return {
        init : function() { counter++; console.log("init called: " + counter); }
    };
}()); 

var t1 = Object.create(twitter);
var t2 = Object.create(twitter);

t1.init();
t2.init();

http://jsfiddle.net/HK8BY/1/

So you just create IEFE (Immediately executed function expression) that returns the desired object. The counter variable is available to the closure of that object’s init function.