JS implements display/hide window fixed position elements as the page scrolls_javascript skills

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.

Let me show you the renderings first:

1.html

<p id="selected-case-count"><span class='form-control'>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();
});
});

The above is the knowledge that the editor has shared with you about JS implementation of displaying/hiding fixed-position elements in windows as the page scrolls. I hope it will be helpful!