PouchDB Interview Questions and Answers for internship

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PouchDB Internship Interview Questions & Answers

  1. What is PouchDB?

    • Answer: PouchDB is an open-source JavaScript database that is a client-side implementation of the CouchDB API. It allows you to create and work with databases within a web browser, providing offline capabilities and synchronization with a CouchDB or other compatible server.

  2. How does PouchDB handle offline functionality?

    • Answer: PouchDB stores data locally in the browser's IndexedDB, localStorage, or WebSQL (depending on browser support). When online, it synchronizes changes with a remote CouchDB server. Changes made offline are queued and applied once connectivity is restored.

  3. Explain the concept of replication in PouchDB.

    • Answer: Replication in PouchDB allows bidirectional synchronization between a local database and a remote database. Changes made in either database are replicated to the other, ensuring data consistency across devices or when offline functionality is involved.

  4. What are the differences between PouchDB and CouchDB?

    • Answer: PouchDB is a client-side JavaScript database that mimics the CouchDB API, while CouchDB is a server-side database. PouchDB works offline, whereas CouchDB requires a network connection. PouchDB replicates with CouchDB to synchronize data.

  5. How do you create a new PouchDB database? Provide an example.

    • Answer: You create a new PouchDB database using the `new PouchDB()` constructor. For example: `let db = new PouchDB('mydb');` This creates a database named 'mydb'.

  6. How do you add a document to a PouchDB database? Provide an example.

    • Answer: You add a document using the `db.put()` method. Example: `db.put({ _id: 'mydoc', name: 'John Doe' }).then(response => {console.log(response)});`.

  7. How do you retrieve a document from a PouchDB database? Provide an example.

    • Answer: You retrieve a document using the `db.get()` method. Example: `db.get('mydoc').then(doc => { console.log(doc); });`

  8. How do you update a document in a PouchDB database? Provide an example.

    • Answer: You update a document by retrieving it, modifying the properties, and then using `db.put()` with the updated document, including the `_rev` property. Example: `db.get('mydoc').then(doc => { doc.name = 'Jane Doe'; return db.put(doc); }).then(response => {console.log(response)});`

  9. How do you delete a document from a PouchDB database? Provide an example.

    • Answer: You delete a document using `db.remove()`, providing both the `_id` and `_rev` properties. Example: `db.get('mydoc').then(doc => { return db.remove(doc); }).then(response => {console.log(response)});`

  10. What is the purpose of the `_id` and `_rev` properties in PouchDB documents?

    • Answer: `_id` is a unique identifier for each document. `_rev` is a revision number that tracks changes to the document; it's crucial for conflict resolution during replication.

  11. Explain the concept of revisions in PouchDB.

    • Answer: PouchDB maintains a history of document revisions. Each change to a document creates a new revision, identified by its `_rev` property. This allows for conflict resolution and rollback if necessary.

  12. How does PouchDB handle conflicts during replication?

    • Answer: When conflicts occur during replication (e.g., the same document is updated on both the client and server), PouchDB typically flags the conflict. You need to resolve the conflict manually by choosing which revision to keep.

  13. What are some common use cases for PouchDB?

    • Answer: Offline-first applications, mobile apps, web applications requiring data persistence even without an internet connection, applications needing data synchronization across multiple devices.

  14. How do you perform a bulk insert of documents into PouchDB?

    • Answer: Use `db.bulkDocs()` to add multiple documents in a single operation. This is more efficient than adding them individually.

  15. How do you query data in PouchDB?

    • Answer: PouchDB uses MapReduce views (similar to CouchDB) for querying. You define a map function to process documents and an optional reduce function to aggregate results. Alternatively, you can use `db.find()` with Mango queries for simpler JSON-based querying (requires PouchDB 7+).

  16. Explain the concept of MapReduce in PouchDB.

    • Answer: MapReduce allows complex data processing. The map function iterates through documents and emits key-value pairs. The reduce function aggregates these emitted values.

  17. How do you create a PouchDB view?

    • Answer: Views are defined using a design document, typically created and updated using `db.put()` on a design document, containing a `map` and optionally a `reduce` function.

  18. How do you use `db.allDocs()` in PouchDB?

    • Answer: `db.allDocs()` retrieves all documents in the database. It's useful for retrieving a list of all documents or when you don't have specific criteria for your query.

  19. What are some common errors encountered when working with PouchDB, and how can they be handled?

    • Answer: Common errors include network issues during replication, conflict resolution, and database corruption. Error handling involves using `.catch()` blocks to handle promises' rejections and implementing strategies for conflict resolution and data recovery.

  20. How can you handle potential data loss in PouchDB?

    • Answer: Implement regular backups, use replication to synchronize data with a remote server, and consider using a persistent storage mechanism like IndexedDB.

  21. What are the advantages of using PouchDB over other client-side databases?

    • Answer: Advantages include its offline capabilities, replication features, familiar CouchDB API, and support for various storage mechanisms (IndexedDB, WebSQL, localStorage).

  22. What are the limitations of PouchDB?

    • Answer: Limitations include potential performance issues with very large datasets, and the need for careful handling of conflicts during replication.

  23. How does PouchDB interact with other JavaScript frameworks/libraries (e.g., React, Angular)?

    • Answer: PouchDB integrates well with various frameworks. You can easily incorporate it into your application's data layer. The database interactions are asynchronous, so you'll handle them using promises or async/await.

  24. Describe your experience with asynchronous programming in JavaScript. How is this relevant to PouchDB?

    • Answer: PouchDB uses promises and asynchronous operations extensively. Familiarity with promises, async/await, and handling asynchronous code is crucial for efficient PouchDB development.

  25. Explain the significance of using promises in PouchDB.

    • Answer: Promises handle asynchronous database operations, allowing your code to continue executing without waiting for long-running database tasks to complete. This ensures responsiveness and avoids blocking the main thread.

  26. What are some best practices for designing PouchDB databases and applications?

    • Answer: Best practices include proper data modeling, efficient query design, error handling, conflict resolution strategies, and regular backups.

  27. How do you test your PouchDB applications?

    • Answer: Testing involves unit tests for individual database operations, integration tests for complex interactions, and end-to-end tests to verify overall application functionality. Consider using a testing framework like Jest or Mocha.

  28. How would you debug issues in a PouchDB application?

    • Answer: Debugging involves using browser developer tools, logging database operations, examining network traffic during replication, and using debugging statements to pinpoint problematic areas.

  29. What are some performance optimization techniques for PouchDB?

    • Answer: Optimization includes efficient query design, minimizing document size, using bulk operations, and properly managing indices (if using Mango queries).

  30. How would you design a PouchDB schema for a specific application scenario (e.g., a to-do list app)?

    • Answer: For a to-do list, you might have a document structure like: `{ _id: UUID, task: '...', completed: true/false, dueDate: '...' }`.

  31. How familiar are you with different database design patterns? How might these apply to PouchDB?

    • Answer: Familiarity with patterns like normalization and denormalization is important. In PouchDB, you'd choose a schema that balances data integrity and query efficiency, considering offline capabilities.

  32. Explain your understanding of the concept of eventual consistency in the context of PouchDB.

    • Answer: Eventual consistency means data will eventually be consistent across all replicated databases, but there may be temporary inconsistencies during replication.

  33. How would you handle security concerns when using PouchDB in a real-world application?

    • Answer: Security involves HTTPS for communication with the remote server, proper authentication and authorization mechanisms, and secure storage of sensitive data, potentially using encryption.

  34. What are some alternative client-side databases to PouchDB, and what are their respective strengths and weaknesses?

    • Answer: Alternatives include IndexedDB directly, Realm, and others. Compare features like offline capabilities, replication support, ease of use, and performance.

  35. What are your preferred tools and techniques for version control in software development? How do they apply to a PouchDB project?

    • Answer: Git is crucial. Version control applies to all code, including database schema migrations (if any).

  36. Describe a challenging problem you faced while working with a database (not necessarily PouchDB), and how you overcame it.

    • Answer: [Describe a specific problem, focusing on the problem-solving process and the solution]

  37. What are your strengths and weaknesses as a developer? How do you think these would apply to this internship?

    • Answer: [Provide a concise and honest assessment of your strengths and weaknesses, linking them to the requirements of the internship.]

  38. Why are you interested in this PouchDB internship?

    • Answer: [Explain your interest in PouchDB, the company, and the internship opportunity.]

  39. What are your salary expectations?

    • Answer: [Provide a realistic salary expectation based on your research and experience.]

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