Source-map fallback

When you click an element on a page that has no Inspekt dev-server running (staging, production, or chrome-extension:// pages), Inspekt can still show source snippets — if you've explicitly opted in to source-map fallback.

Why it's opt-in

Source-map fallback issues additional network requests from your browser to fetch .map files from your app's bundle URLs. Those requests:

• Show up in DevTools (Network tab) and any browser extension that monitors requests.
• Show up in corporate proxy / firewall logs. If you're on a managed network, your IT team will see them.
• Can be multi-megabyte. Source maps for typical React apps are 500 KB–5 MB.
• May fail noisily when the site intentionally doesn't ship source maps.

Inspekt won't make these requests without your consent. The feature is disabled by default. Turn it on in the Chrome extension options under Source map fallback (advanced).

How it works when enabled

1. The capability probe checks every loaded <script src> for a likely adjacent .map.
2. When you click an element, the snippet resolver tries the dev server first. On failure, it falls through to source maps.
3. The resolver fetches the .map file, parses it with @jridgewell/trace-mapping, and matches the desired file path against the map's sources[] array (with path-tail fuzzy matching to handle different build prefixes).
4. The matched sourcesContent[index] is sliced ±N context lines and rendered in the popover. The toolbar badge becomes MAP.

Caching

• Parsed TraceMap instances: LRU bounded at 5 in-memory entries.
• Raw .map text: stored in chrome.storage.session (per-extension session, ~10MB quota, shared across tabs). Evicted on browser restart.
• Negative cache: 404 responses are remembered for the session so Inspekt doesn't re-fetch broken map URLs on every grab.

When to use it

• Inspecting your own staging environment.
• Debugging Chrome extension pages (e.g. your own extension) where there's no dev server but the extension ships source maps with its bundle.
• One-off production triage when source maps happen to be deployed.

When not to use it

• On shared / monitored networks where extra network requests are flagged.
• On production sites you don't own (you're hitting their server with extra requests).
• When source maps aren't deployed (you'll see 404s in DevTools that aren't serving any purpose).