document.body.onbeforeunload = function (event)
{
var c = event || window.event;
if (/webkit/.test(navigator.userAgent.toLowerCase())) {
return "离开页面将导致数据丢失！";
}
else
{
c.returnValue = "离开页面将导致数据丢失！";
原文：http://my.oschina.net/Majw/blog/506818