1 <!DOCTYPE html> 2 <html lang="en"> 3 <head> 4 <meta charset="UTF-8"> 5 <title>Document</title> 6 <style type="text/css"> 7 body{ 8 margin: 0; 9 } 10 .banner{ 11 width: 960px; 12 height: 200px; 13 background-color: cyan; 14 margin: 0 auto; 15 } 16 .menu{ 17 width: 960px; 18 height: 100px; 19 background-color: gold; 20 margin: 0 auto; 21 text-align: center; 22 line-height: 80px; 23 } 24 .menu_back{ 25 width: 960px; 26 height: 100px; 27 margin: 0 auto; 28 display: none; 29 } 30 p{ 31 text-align: center; 32 color: red; 33 } 34 .totop{ 35 height: 60px; 36 width: 60px; 37 background-color: gold; 38 color: #fff; 39 position: fixed; 40 right: 20px; 41 bottom: 50px; 42 line-height: 60px; 43 text-align: center; 44 font-size: 40px; 45 border-radius: 50%; 46 cursor: pointer; 47 display: none; 48 49 } 50 </style> 51 <script type="text/javascript" src="../jquery-1.12.4.min.js"></script> 52 <script type="text/javascript"> 53 $(function(){ 54 var $menu = $('.menu'); 55 var $menu_back = $('.menu_back'); 56 var $totop = $('.totop'); 57 58 $totop.click(function(){ 59 $('html,body').animate({'scrollTop':0},100); 60 }); 61 $(window).scroll(function(){ 62 var iNum = $(document).scrollTop(); 63 if (iNum>200) 64 { 65 $menu.css({ 66 'position':'fixed', 67 'left':'50%', 68 'top':0, 69 'marginLeft':-480 70 }) 71 $menu_back.show(); 72 $totop.show(); 73 } 74 else 75 { 76 $menu.css({ 77 'position':'static', 78 'marginLeft':'auto' 79 }) 80 $menu_back.hide(); 81 $totop.hide(); 82 } 83 }); 84 }); 85 </script> 86 </head> 87 <body> 88 <div class="banner"></div> 89 <div class="menu">菜单</div> 90 <div class="menu_back"></div> 91 <!-- 解决菜单栏处于绝对定位脱离文档流时的bug，设置一个同样大小的div进行占位 --> 92 <div class="totop">↑</div> 93 94 <p>文档内容</p> 95 <br> 96 <br> 97 <br> 98 <br> 99 <br> 100 <br> 101 <br> 102 <br> 103 <br> 104 <br> 105 <br> 106 <br> 107 <p>文档内容</p> 108 <br> 109 <br> 110 <br> 111 <br> 112 <br> 113 <br> 114 <br> 115 <br> 116 <br> 117 <br> 118 <br> 119 <br> 120 <p>文档内容</p> 121 <br> 122 <br> 123 <br> 124 <br> 125 <br> 126 <br> 127 <br> 128 <br> 129 <br> 130 <br> 131 <br> 132 <br> 133 <p>文档内容</p> 134 <br> 135 <br> 136 <br> 137 <br> 138 <br> 139 <br> 140 <br> 141 <br> 142 <br> 143 <br> 144 <br> 145 <br> 146 <p>文档内容</p> 147 <br> 148 <br> 149 <br> 150 <br> 151 <br> 152 <br> 153 <br> 154 <br> 155 <br> 156 <br> 157 <br> 158 <br> 159 <p>文档内容</p> 160 </body> 161 </html>