window.onload = function() {
    var ul = document.getElementById("foo");
    var lis = ul.getElementsByTagName("li");
    for(var i=0; i<lis.length; i++) {
        lis[i].onmouseover = function(x) {
            return function() {
                console.log(x);
            }
        }(i);
    }
};

http://jsfiddle.net/YwtEz/

JavaScript Event Handler Closure

javascript

JavaScript