<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Document</title> <script src="./js/jquery.min.js"></script> <style> .back { position: fixed; width: 50px; height: 50px; background-color: pink; right: 30px; bottom: 100px; display: none; } .container { width: 900px; height: 500px; background-color: skyblue; margin: 400px auto; } </style> </head> <body> <div class="back">返回顶部 </div> <div class="container"></div> <script> $(function() { //被卷起了多少 var boxTop = $(".container").offset().top; $(window).scroll(function() { // console.log(11); //$(document).scrollTop(); console.log($(document).scrollTop()); if ($(document).scrollTop() > boxTop) { $(".back").fadeIn(); } else { $(".back").fadeOut(); } }) //返回顶部 $(".back").click(function() { //$(document).scrollTop(0); $("body,html").stop().animate({ scrollTop: 0 }); }) }) </script> </body> </html>