Rapid fire
Spot the bug in 45 seconds.
Short snippets in JavaScript, Python, Java and C++. Train your eyes to jump straight to the line that's wrong: off-by-ones, coercion traps, async mistakes, shared mutable state, overflow, iterator invalidation and more.
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Unsolved drills come first. Each round: click the buggy line, then pick the diagnosis. 45s per round.
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arrayssortingasyncexpressclosuresequalitycoerciondatesthisloopsserializationobjectsevent loopregexhttpnull safetyfunctionsdictsmathcopyingerrorslistsstringsscopegeneratorsclassesalgorithmslogicrecursioncollectionscontrol flowmoneystreamsconcurrencyboundstypesmemorycontainersinitialisationperformance