Update 404.html

404.html

@@ -19,6 +19,21 @@
   <p class="output">Please try to <a href="javascript:history.back()">go back</a> or <a href="/">return to the homepage</a>.</p>
   <p class="output">Good luck.</p>
 </div>
-
+<script> 
+      const disabledKeys = ["c", "C", "x", "J", "u", "I"]; // keys that will be disabled
+      const showAlert = e => {
+        e.preventDefault(); // preventing its default behaviour
+        return alert("Sorry, you can't view or copy source codes this way!");
+      }
+      document.addEventListener("contextmenu", e => {
+        showAlert(e); // calling showAlert() function on mouse right click
+      });
+      document.addEventListener("keydown", e => {
+        // calling showAlert() function, if the pressed key matched to disabled keys
+        if((e.ctrlKey && disabledKeys.includes(e.key)) || e.key === "F12") {
+          showAlert(e);
+        }
+      });
+</script>
 </body>
 </html>