                        课程
                    
                        /前端开发
                        
                            /jQuery
                        
                        /jQuery基础课程

为什么不行啊求指导啊

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<script src="http://libs.baidu.com/jquery/1.9.0/jquery.js"></script>
<title>挑战题</title>
</head>
<body>
<ul>
<li>111</li>
<li>222</li>
<li>333</li>
<li>444</li>
<li style="display:none" class="hidden">555</li>
<li style="display:none" class="hidden">666</li>
<li>777</li>
</ul>
<input class='button' type='button' value='更多' onclick='click()'>
</body>
<script type="text/javascript">
function click(){
if($(".button").html()=='更多'){
$('.hidden').css("display","block");
$(".button").html("简化");
}else{

$('.hidden').css("display","none");
$(".button").html("更多");
}
}

</script>
</html>