Add first work

w1/p1/app.js

@@ -0,0 +1,21 @@
+"use strict";
+
+/** @type {HTMLElement} */
+let headerElement = null;
+
+const onPageScrolled = function () {
+    if (window.pageYOffset > 0) {
+        headerElement.classList.replace("header__normal", "header__scrolled");
+    } else {
+        headerElement.classList.replace("header__scrolled", "header__normal");
+    }
+}
+
+const init = function () {
+    headerElement = document.querySelector("header");
+    window.addEventListener("scroll", _ => onPageScrolled());
+}
+
+document.addEventListener("DOMContentLoaded", function (event) {
+    init()
+});