Use JS to display/hide window fixed position elements as the page scrolls

The element is displayed at a fixed position in the window. When the page height is greater than a certain height and the page is scrolled down, the element is displayed; when the page position is less than a certain height or the page is scrolled up, the element is hidden. This article will introduce it to you below. JS realizes displaying/hiding the window fixed position element as the page scrolls. Friends who need it can refer to it

Window fixed position display element. When the page height is greater than a certain height and the page scrolls down, the element is displayed; when The element is hidden when the page position is less than a certain height, or when the page scrolls upward.

Let me show you the renderings first:

1.html

<p id="selected-case-count"><span class=&#39;form-control&#39;>已选: <span class="casecount">0</span></span></p>

2.css

p#selected-case-count{
position:fixed; /*固定元素位置*/
top:2px; /*距顶端举例*/
right:40px; /*距右侧位置*/
color:red; 
}

##3.js

$(function() {
$("#selected-case-count").hide();
});
var preTop=0;
var currTop=0;
$(function () {
$(window).scroll(function(){
currTop=$(window).scrollTop();
if(currTop<preTop){
$("#selected-case-count").fadeOut(200);
}elseif ($(window).scrollTop()>600){
$("#selected-case-count").fadeIn(500);
}else{
$("#selected-case-count").fadeOut(500);
}
preTop=$(window).scrollTop();
});
});

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