Implemented URL validation and alert for invalid URLs before sending the request.

script.js

@@ -1,5 +1,14 @@
 const { convertHtmlToMarkdown } = htmlToSMD;
 
+function isValidUrl(string) {
+  try {
+    new URL(string);
+    return true;
+  } catch (_) {
+    return false;
+  }
+}
+
 document
   .getElementById("converter-form")
   .addEventListener("submit", async function (e) {
@@ -7,6 +16,11 @@ document
 
     const urlInput = document.getElementById("url-input").value;
     const markdownOutput = document.getElementById("markdown-output");
+
+    if (!isValidUrl(urlInput)) {
+      alert("Please enter a valid URL");
+      return;
+    }
     const extractMainContent = document.getElementById(
       "extract-main-content"
     ).checked;