js离开或刷新页面检测(且兼容FF,IE,Chrome)

复制代码 代码如下:
<!DOCTYPE html>
<html>
<head>
<script>
  function closeIt()
  {
    return "Any string value here forces a dialog box to \n" +
         "appear before closing the window.";
  }
  window.onbeforeunload = closeIt;
</script>
</head>
<body>
  <a href="https://www.jb51.net">Click here to navigate to
      www.jb51.net</a>
</body>
</html>

兼容FF,IE,Chrome的js离开或刷新页面检测,关键的部分是要有return