javascript 如何检查用户是否在 html 页面的顶部？

how check if user is at the top of the html page?

提问by Lir An

I have a dropdown menu which I like to close automaticly if the user is at the top of the html page,how this can be done with javascript/jquery?

我有一个下拉菜单，如果用户位于 html 页面的顶部，我喜欢自动关闭它，如何使用 javascript/jquery 完成此操作？

回答by Morgan T.

You can easily do this with checking the scrollTopmethod from jQuery, on the window object:

您可以通过检查jQuery 中 window 对象的scrollTop方法轻松做到这一点：

$(window).scrollTop()

Just handle the scroll event and within the function, check $(window).scrollTop() === 0 and you will know if the user is scrolled to the top

只需处理滚动事件并在函数内，检查 $(window).scrollTop() === 0 你就会知道用户是否滚动到顶部

$(document).scroll(function() { 
   if($(window).scrollTop() === 0) {
     $(".menu").hide();
   }
});