使用JavaScript在离开页面前通过onbeforeunload判断并提示用户

 
JavaScript离开页面提示实现代码<!doctype html>
<html lang="cn">
<head>
<meta charset="UTF-8">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>js离开当前页面前判断条件提示是否要离开页面</title>
<script type="text/javascript">
window.onbeforeunload = function() {
{ 
var unloads = document.getElementById("unloads").value;
if(unloads == null || unloads == "") {
return "您确定要退出页面吗？";
} 
} 
}
</script>
</head>
<body>
<input type="text" id="unloads" name="unloads" value="" />
</body>