# Error Handling Errors happen — network failures, null references, invalid input, server outages. The question is not *if* your code will encounter errors, but *how well* it handles them when they occur. ## JavaScript Error Types Know your enemy — five error types and how to handle each: In a catch block, `err` could be any kind of error. Use `err instanceof TypeError` to check the type and respond appropriately. `err.name === 'TypeError'` also works. This lets you show different messages for network failures vs HTTP errors vs validation failures. ## try/catch/finally — Interactive Simulator See how errors propagate and how each block runs: The `finally` block always runs — whether the try succeeded, threw, or the catch handled it. Use it for cleanup that must happen regardless: hiding a spinner, releasing a lock, closing a connection. Never put cleanup only in try — it won't run if an error occurs. ## Fetch Error Handling — Status Codes `fetch()` has two failure modes — understand both: A 404 or 500 response does NOT reject the fetch Promise — it resolves with `res.ok === false`. Always check `if (!res.ok) throw new Error(...)` before calling `res.json()`. Catching a TypeError means no network. Catching your thrown Error means a bad status code. ## Your Challenge Write a `fetchWithHandling(url)` helper that: awaits fetch, checks res.ok (throws on bad status), parses JSON. In the catch block, uses `instanceof` to distinguish network errors from HTTP errors. Create a `class ValidationError extends Error` and throw it from your form validator. Catch it with `err instanceof ValidationError`.