Don't include menu.js if no main menu items

layouts/_default/baseof.html

@@ -36,7 +36,9 @@
 	{{ end }}
 	</div>
 	{{ partial "footer" . }}
+{{- with .Site.Menus.main }}
 <script src="{{ "js/menu.js" | relURL }}"></script>
+{{- end }}
 {{- partial "mathjax.html" . -}}
 </body>
 </html>

static/js/menu.js

@@ -10,6 +10,4 @@ function toggleMenu() {
 	);
 }
 
-if (toggle && menu) {
 toggle.addEventListener('click', toggleMenu, false);
-}