first commit

历届学生/front-end-team-10/项目练习/学生项目/韩孟雪/2023-2-25/js_案例2_淘宝头部定位.html

@@ -0,0 +1,63 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+    <meta charset="UTF-8">
+    <meta http-equiv="X-UA-Compatible" content="IE=edge">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>淘宝头部定位</title>
+    <style>
+        * {
+            margin: 0;
+            padding: 0;
+        }
+
+        body {
+            height: 3000px;
+        }
+
+        .head {
+            width: 100%;
+            height: 60px;
+        }
+
+        .head_menu {
+            width: 100%;
+            height: 50px;
+            background: #e3bcbc;
+            /* margin: 0 auto; */
+        }
+    </style>
+</head>
+
+<body>
+    <div class="head"> </div>
+    <div class="head_menu"></div>
+</body>
+<script>
+    // 给网页绑定滚动事件
+    // 获取滚动条的滚动距离，然后拿滚动距离进行判断 document.documentElement.scrollTop
+    // 大于 某个数值 ，给  html 定固定定位，反之不加
+    var body = $("body"), head_menu = $(".head_menu");
+
+    body.onscroll = () => {
+        var offsetTop = document.documentElement.scrollTop;
+       // console.log("offsetTop: ", offsetTop);
+       if(offsetTop >60 ){
+            head_menu.style.position = "fixed"
+            head_menu.style.top = "0"
+       }else{
+        head_menu.style.position = "static"
+       }
+    }
+
+    function $(className) {
+        return document.querySelector(className);
+    }
+    function _(className) {
+        return document.querySelectorAll(className);
+    }
+
+</script>
+
+</html>