How Race Conditions Threaten Backend Systems and Ways to Fix Them in Express.js

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Race conditions occur when multiple simultaneous requests access and modify the same shared data, producing unpredictable or incorrect outcomes that depend on execution timing. Common real-world consequences include oversold inventory, duplicate financial transactions, incorrect account balances, and conflicting profile updates. In Express.js, asynchronous operations such as database queries and API calls make applications especially vulnerable, since checks and writes can interleave across concurrent requests. Developers can mitigate these issues using database transactions, mutex locks, or idempotency keys, each carrying trade-offs in complexity, latency, or throughput. Choosing the right strategy depends on the specific operation, making race condition awareness a critical skill for backend engineers.

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