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Grokking Node.js Design Patterns for Interviews

Solution: Add Logging to a Utility Function

Explore how to apply the decorator pattern to add logging to a pure utility function in Node.js. This lesson helps you understand wrapping functions to log input arguments and return values without altering the original function, enhancing traceability while preserving core behavior.

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Solution explanation

  • Lines 1–3: square(n) is a pure utility function that simply returns n * n. It’s untouched and unaware of logging.

  • Lines 6–13: withLogging(fn) is a functional decorator. It wraps the original function:

    • Logs the arguments before calling fn(...). ...