Advanced Debugging

For problems that only appear in production (and can't be easily reproduced locally), two techniques go beyond browser devtools:

• Structured logging with consistent, searchable fields, so a real incident can be traced through a huge volume of log lines from a live server.
• Source maps — deployed JavaScript is usually minified; uploading its source map lets error-tracking tools (like Sentry) show the original, readable source location of a production crash, not the minified one.

The underlying discipline is the same as Level 1's debugging lesson — reproduce, narrow down, fix — just with better tools for problems too large or too rare to step through by hand.