Error Handling

Detailed Explanation

Error Handling is the practice of writing code that anticipates things going wrong and responds gracefully instead of crashing. In a fullstack app, errors happen everywhere — Database queries fail, networks drop, users submit bad data — and good error handling ensures your Web Application stays usable.

The fundamental pattern is Try/Catch:

try {
  const { data, error } = await supabase.from('posts').select('*');
  if (error) throw error;
  return { posts: data };
} catch (err) {
  console.error('[ERROR] Failed to load posts:', err.message);
  return { error: "Couldn't load posts. Please try again." };
}

In React Router apps, error handling works at multiple levels:

1. Loader and Action level: Try/Catch blocks catch Database and network errors, returning user-friendly messages
2. Component level: useActionData displays Validation errors from form submissions
3. Page level: Error boundaries catch crashes and show fallback UI instead of blank pages
4. Logging level: console.error() and Supabase logs record what went wrong for Debugging

There are two categories of errors: expected errors (empty forms, expired tokens, permission issues) that you can predict and handle with Validation and user messages, and unexpected errors (server crashes, network outages) that you catch with Try/Catch and error boundaries.

The goal isn't to prevent all errors — it's to make sure no error crashes the app and every error gives the user a clear next step.

Common errors to handle: undefined values when data is missing, Permission denials from RLS Policies, and unexpected responses from Supabase or Edge Functions.