problem description: when you click .nav _ li, get the child element ul in .nav _ li, and then add the nav_li_on_2 class attribute to it. When I click on other peer buttons of .nav _ li, I will remove the class attribute added by ul in the current .nav _ li, but the following code can only be added and not deleted.
<script type="text/javascript">
// JS
$(document).ready(function(){
$(".nav_li").click(function(){
$(this).find("ul").addClass("nav_li_on_2").siblings(".nav_li_on_2").removeClass("nav_li_on_2")
})
})
</script>