counter

counter.js

function counter() {
    var count = 1;
    return function() {
        alert(count++);
    }
}

counter.txt

Each can increment count variable despite the fact that we're outside the scope of the count() function.

var foo = {}, bar = {};
foo.count = counter();
bar.count = counter();
foo.count(); // alerts "1"
bar.count(); // alerts "1"
foo.count(); // alerts "2"
bar.count(); // alerts "2"