Increment count with unique visitor ID stored in localStorage.

assets/js/increment-count.js

@@ -1,7 +1,34 @@
+const STORAGE_KEY = "yasuaki640.github.io-visitorId";
+const CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
+
+const generateRandomString = (length) => {
+  let res = "";
+  const charLength = CHARS.length;
+  for (let i = 0; i < length; i++) {
+    res += CHARS.charAt(Math.floor(Math.random() * charLength));
+  }
+
+  return res;
+};
+
+const retrieveVisitorId = () => {
+  const visitorId = localStorage.getItem(STORAGE_KEY);
+  if (!visitorId) {
+    localStorage.setItem(STORAGE_KEY, generateRandomString(16));
+  }
+
+  return visitorId;
+};
+
 (async () => {
-  const res = await fetch(
+  const visitorId = retrieveVisitorId();
+
+  const url = new URL(
     "https://page-view-counter-api.yasuaki640.workers.dev/increment-count",
   );
+  url.searchParams.append(STORAGE_KEY, visitorId);
+
+  const res = await fetch(url);
   const { count } = await res.json();
 
   document.getElementById(