页面离开前提示用户(onbeforeunload 事件)
window.onbeforeunload = function (e) {
var evt = e || window.event;
evt.returnValue = '离开会使编写的内容丢失';
}
window.onbeforeunload = function (e) {
var evt = e || window.event;
evt.returnValue = '离开会使编写的内容丢失';
}