Deno Interview Questions and Answers for 10 years experience

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Deno Interview Questions (10 Years Experience)

  1. What are the key differences between Deno and Node.js?

    • Answer: Deno uses V8 engine like Node.js but is built in Rust, offering improved memory safety and performance. It uses TypeScript by default, has built-in support for many modules (like `std`), employs a secure default execution environment (no automatic access to filesystem etc.), uses ES modules, and offers a better developer experience with features like top-level `await`.

  2. Explain Deno's module system. How does it differ from Node.js's require()?

    • Answer: Deno uses ES modules, importing modules using URLs or file paths. This contrasts with Node.js's `require()`, which uses a path-based system and often leads to complexities with version management and module resolution. Deno's URL-based imports are more explicit and facilitate better version control and remote module fetching.

  3. How does Deno handle permissions? Describe the `--allow-` flags.

    • Answer: Deno's security model is centered around explicit permissions. By default, Deno restricts access to system resources like the network, filesystem, and environment variables. The `--allow-` flags (e.g., `--allow-read`, `--allow-net`, `--allow-env`) grant specific permissions to the script, enhancing security by only granting what's needed.

  4. Explain how to use the Deno standard library (`std`). Give an example.

    • Answer: The `std` library provides many built-in modules. You import them using URLs, e.g., `import { serve } from "https://deno.land/std@0.204.0/http/server.ts";`. This example imports the `serve` function from the HTTP server module. The versioning (`@0.204.0`) ensures using a specific, compatible version.

  5. How can you handle asynchronous operations in Deno? Provide examples with `async`/`await` and promises.

    • Answer: Deno fully supports `async`/`await` and promises. `async` functions define asynchronous operations, and `await` pauses execution until a promise resolves. Example: `async function fetchData() { const response = await fetch("https://example.com"); return await response.text(); }`

  6. What are the benefits of using TypeScript with Deno?

    • Answer: TypeScript's static typing helps catch errors early during development, improving code maintainability and reducing runtime errors. Deno's built-in TypeScript support simplifies setup and integrates seamlessly with its module system.

  7. How do you handle errors in Deno? Discuss different approaches.

    • Answer: Deno uses standard JavaScript `try...catch` blocks for error handling. You can also utilize custom error types and handle specific exceptions. For asynchronous operations, `try...catch` works within `async` functions.

  8. Explain the concept of top-level `await` in Deno.

    • Answer: Top-level `await` allows you to use `await` directly in the top-level scope of a module without needing to wrap it in an `async` function. This simplifies asynchronous code structure, making it cleaner and more readable.

  9. How do you test your Deno code? Discuss testing frameworks and strategies.

    • Answer: Deno supports several testing frameworks, including its built-in `Deno.test()` function and third-party options like `uvu` or `vitest`. Common strategies include unit testing individual functions, integration testing modules, and end-to-end testing of the entire application. Testing involves writing assertions to verify the correctness of the code.

  10. Describe your experience with dependency management in Deno.

    • Answer: Deno's dependency management is streamlined by directly importing modules via URLs. This eliminates the need for package managers like npm or yarn, simplifying dependencies and reducing the complexity of lock files and version management. You specify the version directly in the import statement.

  11. How would you deploy a Deno application?

    • Answer: Deployment strategies for Deno applications vary depending on the application type and its requirements. Options include using a serverless platform (e.g., AWS Lambda, Vercel), deploying to a VPS, Docker containers, or simply bundling the application using tools like `deno bundle` and deploying it as a single executable.

  12. Explain how you would debug a Deno application.

    • Answer: Deno offers built-in debugging tools, including a debugger that can be launched with the `--inspect` flag. This enables attaching a debugger (like the Chrome DevTools) to inspect variables, set breakpoints, and step through code. Console logging (`console.log()`) is also essential for debugging and identifying issues.

  13. What are some best practices for writing efficient and maintainable Deno code?

    • Answer: Best practices include using TypeScript for static typing, following consistent coding style guidelines, using descriptive variable and function names, writing modular code, thorough testing, and leveraging the `std` library where appropriate.

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