Update index.html

index.html

@@ -20,6 +20,9 @@
           <li> You don't need to answer every question in the same session. Feel free to start and stop when convenient! </li>
         </ul>
         <p> Use the <strong>same email</strong> each time to save your progress. Thanks again for participating! </p>
+        <div class="alert alert-danger" role="alert" id="email warning" style="display: none;">
+          Provide an email, please!
+        </div>
         <input type="text" id="email" placeholder="Email"/>
         <br /> <br />
         <button id="submit" onclick="launch();"><strong>Let's go!</strong></button>
@@ -28,8 +31,7 @@
       function launch() {
         var email = document.getElementById("email").value;
         if (email == "") {
-          // warning message
-          alert("No email provided :(");
+          document.getElementById("email warning").style.display = "block";
         } else {
           alert("Email found " + email);
         }