前端小案例——导航回顶部（HTML+CSS+JS, 附源码）

一、前言

实现功能：

这个案例实现了页面滚动到一定位置时显示"回到顶部"按钮，并且点击按钮能够平滑滚动回页面顶部的功能。

实现逻辑：

页面结构：通过HTML标签定义了页面的基本结构。页面主要由多个div.content组成，每个div都有不同的背景颜色，用来模拟页面内容。此外，还有一个div.nav作为侧边的导航栏，里面包含了几个列表项（li），每个列表项都有一个图标（使用svg）和文字描述（p标签），用来表示不同的功能。
样式设计：通过CSS设置了页面的样式。这包括对页面内容、导航栏以及导航项的样式设定，如位置、大小、颜色等。特别地，back-to-top按钮（回顶部）默认是不显示的（display: none;），只有当页面滚动到一定程度时才会显示出来。
交互逻辑：通过JavaScript添加了页面的交互功能。
- 监听scroll事件：当页面滚动时，检查页面的垂直滚动位置（window.scrollY或document.documentElement.scrollTop）。如果滚动位置超过300px，则显示回顶部按钮；否则，隐藏该按钮。
- 监听回顶部按钮的点击事件：当点击回顶部按钮时，页面平滑滚动到顶部。这是通过调用window.scrollTo方法并设置top: 0以及behavior: 'smooth'来实现的，其中top: 0意味着滚动到页面顶部，behavior: 'smooth'则使得滚动过程平滑进行。

二、项目运行效果

三、全部代码

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><title>导航回顶部</title><style>*{margin: 0;padding: 0;text-decoration: none;list-style: none;background-repeat: no-repeat;}.content{margin: 0 auto;width: 70%;height: 600px;}.nav{position: fixed;right: 10px;bottom: 50%;transform: translateY(50%);z-index: 9;background-color: #F7F9FA;box-shadow: -2px 0 5px 2px rgba(97, 105, 119, 0.18);border-radius: 18px 0 0 18px;width: 60px;}.nav_box{padding: 26px 0;text-align: center;}.nav_box p{font-size: 12px;color: #333;line-height: 17px;}.nav_box li{cursor: pointer;margin-top: 36px;}</style>
</head>
<body><div class="content" style="background-color: rgb(191, 209, 248);"></div><div class="content" style="background-color: pink;"></div><div class="content" style="background-color: rgb(190, 250, 245);"></div><div class="content" style="background-color: rgb(250, 228, 200);"></div><div class="content" style="background-color: rgb(241, 204, 254);"></div><div class="content" style="background-color: rgb(255, 128, 162);"></div><div class="nav"><ul class="nav_box"><li style="margin-top: -5px;"><svg t="1706775929643" class="icon" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="1819"width="24" height="24"><pathd="M948.168406 510.186701 531.992845 126.667911c-10.704806-9.834996-27.224038-9.727549-37.81935 0.107447L75.714937 516.272303c-11.248182 10.486842-11.845793 28.092825-1.412163 39.339983 5.487991 5.868661 12.932544 8.856715 20.377096 8.856715 6.792707 0 13.58439-2.444679 18.96391-7.443529l98.732675-91.885733L212.376457 876.833219c0 15.32401 12.443403 27.821649 27.821649 27.821649l182.087105 0c7.390317 0 14.508435-2.933819 19.724227-8.259104 5.216815-5.216815 8.096399-12.280698 8.096399-19.671015l-0.76134-224.660736 132.095527 0-2.879584 224.335325c-0.107447 7.498788 2.771113 14.671141 8.042163 19.996426 5.216815 5.216815 12.334933 8.259104 19.778462 8.259104l185.619558 0c15.377222 0 27.821649-12.497639 27.821649-27.821649L819.822272 467.639676l90.636277 83.518159c11.247158 10.324136 28.907377 9.617032 39.339983-1.63115C960.177927 538.224268 959.470823 520.619308 948.168406 510.186701zM764.178975 418.191474l0 430.820096L634.583384 849.01157l2.879584-224.388537c0.107447-7.444553-2.771113-14.616906-8.042163-19.942191-5.216815-5.270027-12.334933-8.259104-19.778462-8.259104l-188.226942 0c-7.390317 0-14.508435 2.933819-19.724227 8.205892-5.216815 5.216815-8.096399 12.334933-8.096399 19.724227l0.760317 224.660736L268.018731 849.012593 268.018731 415.855266c0-0.760317-0.38067-1.357927-0.434905-2.118244l245.662049-228.6547L764.505409 416.615583C764.451174 417.158958 764.178975 417.649122 764.178975 418.191474z"fill="#231815" p-id="1820"></path></svg><p>首页</p></li><li><svg t="1706776076434" class="icon" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="3101"width="24" height="24"><pathd="M966.5 345.4c-30.3-91.7-89.1-173.9-166.6-232.4-83.5-63-183-96.3-287.9-96.3S307.6 50 224.1 113C146.6 171.4 87.8 253.6 57.5 345.4c-34 13-57.5 46-57.5 83.1v133.6c0 41.7 29.6 78.3 70.4 87 6.2 1.3 12.4 2 18.6 2 49.1 0 89-39.9 89-89V428.5c0-43.2-31-79.3-71.9-87.3 63.3-166.2 226-280 405.8-280s342.5 113.7 405.8 280c-40.9 8-71.9 44.1-71.9 87.3v133.6c0 39 25.2 72.1 60.2 84.1C847.8 772.1 732.3 863 596.3 889.8c-11.8-35.5-45.1-60.7-84.3-60.7-49.1 0-89 39.9-89 89s39.9 89 89 89c43.5 0 79.7-31.4 87.5-72.7 158.1-29.2 291.6-136.8 353.9-285.5h0.2c40.8-8.8 70.4-45.4 70.4-87V428.5c0-37.1-23.5-70.1-57.5-83.1z m-832.9 83.1v133.6c0 24.6-20 44.5-44.5 44.5-3.1 0-6.2-0.3-9.3-1-20.4-4.4-35.2-22.7-35.2-43.5V428.5c0-20.8 14.8-39.1 35.2-43.5 3.1-0.7 6.2-1 9.3-1 24.5 0 44.5 20 44.5 44.5zM512 962.8c-24.5 0-44.5-20-44.5-44.5s20-44.5 44.5-44.5c23.9 0 43.4 18.8 44.4 42.7 0 0.6 0.1 1.1 0.1 1.8 0 24.5-20 44.5-44.5 44.5z m467.5-400.7c0 20.8-14.8 39.1-35.2 43.5-2.2 0.5-4.6 0.8-7.5 0.9-0.6 0-1.2 0.1-1.8 0.1-24.5 0-44.5-20-44.5-44.5V428.5c0-24.5 20-44.5 44.5-44.5 3.1 0 6.2 0.3 9.3 1 20.4 4.4 35.2 22.7 35.2 43.5v133.6z"p-id="3102"></path><pathd="M682.7 656.6c9.2-8.2 9.9-22.3 1.7-31.4-8.2-9.2-22.3-9.9-31.4-1.7-149.1 133.5-275.2 6.9-280.7 1.2-8.5-8.9-22.6-9.2-31.5-0.7-8.9 8.5-9.2 22.6-0.7 31.5 1.1 1.1 72.2 73.6 173.3 73.6 50.6-0.1 108.7-18.3 169.3-72.5z"p-id="3103"></path></svg><p>客服</p></li><li><svg t="1706776191957" class="icon" viewBox="0 0 1060 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="4153"width="24" height="24"><pathd="M963.2 408c-13.6 0-24 11.2-24 24v432c0 27.2-21.6 48.8-48.8 48.8H159.2c-27.2 0-48.8-21.6-48.8-48.8V159.2c0-27.2 21.6-48.8 48.8-48.8h470.4c13.6 0 24-11.2 24-24 0-13.6-11.2-24-24-24H154.4C103.2 62.4 61.6 104 61.6 155.2v715.2c0 51.2 41.6 92.8 92.8 92.8h740.8c51.2 0 92.8-41.6 92.8-92.8V432c0-12.8-11.2-24-24.8-24z"fill="" p-id="4154"></path><pathd="M968 151.2l-44-44c-30.4-30.4-78.4-33.6-105.6-5.6L355.2 564.8 510.4 720l463.2-463.2c28-27.2 25.6-75.2-5.6-105.6z m-116.8 159.2l-344 344-86.4-85.6 345.6-345.6 84.8 87.2z m88-88l-51.2 51.2-85.6-86.4 50.4-50.4c10.4-10.4 28.8-9.6 40 2.4l44 44c12 10.4 12.8 28.8 2.4 39.2zM355.2 566.4l-48 174.4c-2.4 8 0 16 5.6 21.6 5.6 5.6 13.6 8 21.6 5.6l174.4-48-36-36L360 715.2l31.2-113.6-36-35.2z"fill="" p-id="4155"></path></svg><p>反馈</p></li><li><svg t="1706776564791" class="icon" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="8157"width="24" height="24"><pathd="M512 358.555826c-12.288 0-22.26087 9.97287-22.26087 22.26087l0 268.221217c0 12.288 9.97287 22.26087 22.26087 22.26087s22.26087-9.97287 22.26087-22.26087L534.26087 380.816696C534.26087 368.528696 524.288 358.555826 512 358.555826zM512 716.176696c-12.288 0-22.26087 9.97287-22.26087 22.26087l0 44.699826c0 12.288 9.97287 22.26087 22.26087 22.26087s22.26087-9.97287 22.26087-22.26087l0-44.699826C534.26087 726.149565 524.288 716.176696 512 716.176696zM998.912 867.394783 575.688348 131.33913C559.972174 104.025043 536.754087 88.33113 512 88.33113S464.027826 104.025043 448.311652 131.33913L25.088 867.394783c-8.859826 15.426783-13.356522 30.675478-13.356522 45.345391 0 32.456348 23.908174 65.224348 77.312 65.224348l845.913043 0c53.381565 0 77.289739-32.768 77.312-65.224348C1012.268522 898.070261 1007.771826 882.821565 998.912 867.394783zM934.956522 933.420522 89.043478 933.420522c-9.861565 0-32.790261-2.025739-32.790261-20.702609 0-6.678261 2.56-14.669913 7.41287-23.129043L486.912 153.533217c15.137391-26.290087 35.06087-26.290087 50.198261 0l423.223652 736.033391c4.85287 8.45913 7.41287 16.450783 7.41287 23.129043C967.746783 931.394783 944.818087 933.420522 934.956522 933.420522z"fill="#2c2c2c" p-id="8158"></path></svg><p>举报</p></li><li class="back-to-top"><svg t="1706776294481" class="icon" viewBox="0 0 1024 1024" version="1.1" xmlns="http://www.w3.org/2000/svg" p-id="6256"width="24" height="24"><pathd="M153.979 174.004h718.833c16.142 0 29.127-12.986 29.127-29.127s-12.986-29.127-29.127-29.127h-718.833c-16.142 0-29.127 12.986-29.127 29.127s12.986 29.127 29.127 29.127zM533.845 246.701c-11.408-11.408-29.855-11.408-41.142 0l-351.952 351.952c-11.408 11.408-11.408 29.855 0 41.142 5.703 5.703 13.107 8.496 20.631 8.496s14.928-2.791 20.631-8.496l302.194-302.194v542.614c0 16.142 12.986 29.127 29.127 29.127s29.127-12.986 29.127-29.127v-542.614l302.194 302.194c5.703 5.703 13.107 8.496 20.631 8.496s14.928-2.791 20.631-8.496c11.408-11.408 11.408-29.855 0-41.142l-352.074-351.952z"fill="" p-id="6257"></path></svg><p>回顶部</p></li></ul></div><script>let backToTopBtn = document.querySelector('.back-to-top');backToTopBtn.style.display = 'none';window.addEventListener('scroll', () => {if (window.scrollY > 300 || document.documentElement.scrollTop > 300) {backToTopBtn.style.display = 'block';} else {backToTopBtn.style.display = 'none';}});backToTopBtn.addEventListener('click', (e) => {e.preventDefault();window.scrollTo({top: 0,behavior: 'smooth'});});</script>
</body>
</html>