Answer
A special middleware with four parameters used to catch and manage errors in Express apps.
Quick Answer
Error-handling middleware in Express has four parameters (err, req, res, next) — Express knows it's an error handler by the arity. Define it last, after all routes. When you call next(err) anywhere, Express skips to this handler. It catches any error passed to next() and lets you format and return consistent error responses.
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Verified Answer
This answer has been peer-reviewed by industry experts holding senior engineering roles to ensure technical accuracy and relevance for modern interview standards.
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Source: SugharaIQ