12.1 使用可折叠菜单
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script>
function change() {
var element = document.getElementById("menu");
if (element.style.display == "block") {
element.style.display = "none";
} else {
element.style.display = "block";
}
}
</script>
</head>
<body>
<button onclick="change()">选择项</button>
<ul id="menu" class="menu" style="display: none;">
<li><a href="https://www.baidu.com">百度</a></li>
<li><a href="https://www.google.com">Google</a></li>
</ul>
</body>
</html>