var body = document.querySelector('body'),
lis = document.getElementsByTagName('li');

body.addEventListener('click', function (event) {
var event = event || window.event;
var tisTag = event.srcElement || event.target;
for (var i = 0; i < lis.length; i++) {
var li = lis[i];
if (li.contains(tisTag)) {
alert('li 被点击了！');
}
}
});