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Grokking Node.js Design Patterns for Interviews

Solution: Lazy-Load a Heavy Service Only When First Used

Discover how to implement lazy loading for resource-intensive services in Node.js by applying the Proxy pattern. This lesson teaches you to defer service initialization until the first method or property access, improving startup performance without changing how modules interact with the service. You will understand the practical use of the Proxy get trap to control object creation dynamically.

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Solution explanation

  • Lines 2–10: We define the DataService class to simulate an expensive dependency.

    • Its constructor logs a message when initialized, representing heavy setup work.

    • The fetchData() method represents an operation that other modules will eventually call.

  • Lines 13–26: The createLazyService() function builds the Proxy responsible for lazy initialization.

    • A variable instance holds the actual DataService instance, starting as null.

    • The ...