Managing Routing Issues for Nonexistent Contacts

Now that we have routing implemented, we need to manage routing issues. Notably, displaying an error message when a user loads the URL for a nonexistent contact, e.g., #contacts/999 or #contacts/foo. Right now, our app will display a blank page, which isn’t very helpful.

We’ll need a new template to display our error message. Let’s add it to index.html: