Javascript self executing functions and variable scope

Could someone explain to me this behavior?

var obj = function()
{
    var _bar = 10;
    function i_bar(){return ++_bar;}

    return {
        bar  : _bar,
        i_bar: i_bar
    }
}();

obj.bar     // prints 10, OK
obj.i_bar() // prints 11, OK
obj.bar = 0 // prints 0,  OK
obj.i_bar() // prints 12, NOK

Since the only variable is _bar, shouldn't the last obj.i_bar() have printed 1 instead of 12?

Your bar is not the same references as what i_bar is referencing. Value types are not by reference, so you are copying bar into the return object, but it is not the bar that your function is referring to. Try this:

var obj = function()
{
    var self = this;

    function i_bar(){return ++self.bar;}

    self.bar = 10;
    self.i_bar = i_bar;

    return self;
}();