JS Function closures for persistent memory

[dvas0004]

Javascript functions can return other functions, and the inner function has access to the scope of the outer function, making it useful to store variables persistently between function calls, for example:

var checkCookie = function() {
    var lastCookie = document.cookie; // 'static' memory between function calls
    return function() {
        var currentCookie = document.cookie;

        if (currentCookie != lastCookie) {
            // something useful like parse cookie, run a callback fn, etc.
            lastCookie = currentCookie; // store latest cookie
        }
    };
}();
window.setInterval(checkCookie, 100); // run every 100 ms

[dvas0004]

https://stackoverflow.com/questions/14344319/can-i-be-notified-of-cookie-changes-in-client-side-javascript