OnBeforeUnload

gistfile1.js

var OnBeforeUnload = (function(){
    var
    FDUM = new Function,
    AFFIRM = function(){ return true; };

 

    var _reg = function(msg,opts){
        opts = opts || {};
        var
            pid = null,
            pre = typeof opts.prefire == 'function' ? opts.prefire : FDUM,
            callback = typeof opts.callback == 'function' ? opts.callback : FDUM,
            condition = typeof opts.condition == 'function' ? opts.condition : AFFIRM;

 

        window.onbeforeunload = function(){
            return condition() ? (pre(),setTimeout(function(){ pid = setTimeout(callback,20); },1),msg) : void 0; 
        }

 

        window.onunload = function(){ clearTimeout(pid); };

 

    }

 

    var _unreg = function(){ window.onbeforeunload = null;  }

 

    return {
        register : _reg,
        unregister : _unreg
    };

 

})();

 

OnBeforeUnload.register('Hello!',{ 
    condition:function_that_returns_true_to_fire_event_false_to_ignore,
    prefire:function_to_call_on_page_exit_attempt, 
    callback:function_to_call_if_user_stays
});