封锁浏览器前出发事件

关闭浏览器前出发事件

<a href="javascript:;">点我一下</a><a href="javascript:alert('test');">点我一下</a><a href="###" onclick="alert('test');">点我一下</a><script type="text/javascript">//<![CDATA[window.onbeforeunload = function(e){  return 'leave or stay';}window.onunload = function(){  alert('onunload');}//]]></script>