add topic_4

topic_4/example1/script.js

@@ -0,0 +1,23 @@
+window.onload = function() {
+    let nav = document.getElementById("nav")
+    let items = nav.getElementsByClassName("menu-item");
+    for (let i = 0; i < items.length; i++) {
+        let item = items[i]
+        item.onclick = function () {
+            for (let j = 0; j < items.length; j++) {
+                if (i === j) {
+                    continue
+                }
+                let oldItem = items[j]
+                oldItem.getElementsByClassName("submenu")[0].classList.remove('show')
+            }
+
+            let submenu = item.getElementsByClassName("submenu")[0];
+            if (submenu.classList.contains('show')) {
+                submenu.classList.remove('show')
+            } else {
+                submenu.classList.add('show')
+            }
+        }
+    }
+}