Deno Interview Questions and Answers for 5 years experience

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Deno Interview Questions (5 Years Experience)

  1. What is Deno, and how does it differ from Node.js?

    • Answer: Deno is a JavaScript/TypeScript runtime built on V8, similar to Node.js. Key differences include Deno's use of TypeScript out of the box, its secure-by-default approach (requiring explicit permissions for network access, file system access, etc.), its built-in dependency management (using URLs instead of `npm`), and its support for ES modules. Node.js, conversely, relies heavily on npm for package management, has a more permissive security model, and traditionally favors CommonJS modules although ES modules are now well-supported.

  2. Explain Deno's module resolution system.

    • Answer: Deno uses ES modules, resolving them based on URLs. This eliminates the complexities of `node_modules` and allows for easy version control and dependency management. It can resolve modules from remote URLs, local files, or even from a bundled `deno.land/x` repository.

  3. How does Deno handle permissions?

    • Answer: Deno employs a secure-by-default approach. By default, it does not allow access to the network, file system, or environment variables. These permissions must be explicitly granted using command-line flags (e.g., `--allow-net`, `--allow-read`, `--allow-write`, `--allow-env`). This enhances security and prevents accidental data leaks or unauthorized modifications.

  4. What are the benefits of using TypeScript in Deno?

    • Answer: Deno's built-in support for TypeScript provides several advantages. Static typing helps catch errors during development, improving code maintainability and reducing runtime issues. TypeScript also enhances code readability and allows for better collaboration among developers due to the improved code clarity and type safety.

  5. How do you manage dependencies in Deno?

    • Answer: Dependencies in Deno are managed by importing them directly using URLs. This avoids the complexity of `package.json` and `npm` or `yarn`. For example, you might import a module using `import { someFunction } from "https://deno.land/std/some_module.ts";`.

  6. Explain the purpose of Deno's `std` module.

    • Answer: The `std` module (located at `https://deno.land/std`) provides a standard library for Deno, offering various utility functions and modules for common tasks like file system operations, networking, and more. It’s a curated collection of useful modules, analogous to Python’s standard library.

  7. Describe the use of `Deno.run()` or `Deno.spawn()`.

    • Answer: `Deno.run()` and `Deno.spawn()` are used to execute external commands. `Deno.run()` provides more control, allowing for managing standard input, output, and error streams, while `Deno.spawn()` is simpler for less complex scenarios. They're crucial for tasks like running system commands or interacting with external tools within a Deno application.

  8. How can you test your Deno code?

    • Answer: Deno supports testing natively. You can write test files (typically with a `.test.ts` extension) that use Deno's built-in testing framework. Tests are typically organized using `Deno.test()` functions, allowing for easy unit and integration testing. The test runner is invoked using `deno test`.

  9. What are some best practices for writing secure Deno applications?

    • Answer: Best practices for secure Deno applications include minimizing the use of `--allow` flags to only what's strictly necessary, validating all user inputs carefully to prevent vulnerabilities like cross-site scripting (XSS) or SQL injection, using appropriate data sanitization techniques, and regularly updating dependencies to patch security flaws. Also, be extremely cautious when granting network access permissions and always adhere to the principle of least privilege.

  10. Explain how to use Deno's `fetch` API.

    • Answer: Deno's `fetch` API is similar to the browser's `fetch` API and is used for making HTTP requests. It's asynchronous and returns a promise that resolves to the response. You use it to retrieve data from a server, send data to a server, etc. Requires `--allow-net` permission. Example: `const response = await fetch('https://example.com'); const data = await response.json();`

  11. [Question 11]

    • Answer: [Answer 11]

  12. [Question 12]

    • Answer: [Answer 12]

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