first commit

历届学生/font-end-nine/项目练习/学生项目/郑若怡/案例练习/上课练习/滚动.html

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+<!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>Document</title>
+    <style>
+        body {
+            height: 30000px;
+        }
+
+        .header {
+            width: 100%;
+            height: 50px;
+            background: red;
+        }
+
+        .fixed {
+            position: fixed;
+            width: 100%;
+            left: 0;
+            top: 0;
+        }
+    </style>
+</head>
+
+<body>
+    <div class="header"></div>
+</body>
+<script>
+    // var header = $(".header");
+    // $("body").onscroll = function () {
+    //     if (document.documentElement.scrollTop > 100) {
+    //         header.className = "header fixed"
+    //     } else {
+    //         header.className = "header"
+    //     }
+    //     console.log("页面被滚动了");
+    // }
+
+
+    var header = $(".header")
+    $("body").onscroll = function () {
+        if (document.documentElement.scrollTop > 100) {
+            header.className = "header fixed"
+        } else {
+            header.className = "header"
+        }
+    }
+
+
+
+
+    function $(className) {
+        return document.querySelector(className)
+    }
+</script>
+
+</html>