WebAssembly Interview Questions and Answers for internship

1. What is WebAssembly (Wasm)?

   • Answer: WebAssembly is a binary instruction format for a stack-based virtual machine. It's designed as a portable compilation target for programming languages, enabling high-performance applications on the web. It aims to provide near-native performance while maintaining security and portability across different browsers and platforms.

2. What are the advantages of using WebAssembly?

   • Answer: Advantages include significantly improved performance compared to JavaScript for computationally intensive tasks, better security due to its sandboxed environment, portability across different browsers and platforms, and the ability to reuse existing codebases written in languages like C++, Rust, and Go.

3. What are the disadvantages of using WebAssembly?

   • Answer: Disadvantages include a steeper learning curve compared to JavaScript, the need for a compilation step, potential debugging challenges, and limited access to browser APIs directly (although this is improving with WebAssembly System Interface - WASI).

4. Explain the WebAssembly module lifecycle.

   • Answer: The lifecycle involves compilation (from source code to Wasm binary), loading (into the browser), instantiation (creating an instance of the module), execution (running the module's functions), and finally, potentially unloading (releasing resources).

5. How does WebAssembly interact with JavaScript?

   • Answer: WebAssembly modules can import and export functions, allowing them to seamlessly interact with JavaScript. JavaScript code can call Wasm functions, and vice-versa. This interoperability is crucial for integrating Wasm into existing web applications.

6. What are WebAssembly memory and tables?

   • Answer: WebAssembly memory is a linear array of bytes that provides a way for Wasm modules to store and access data. Tables are arrays of function references, primarily used for indirect function calls, enabling dynamic dispatch.

7. What are the different WebAssembly value types?

   • Answer: Basic value types include i32 (32-bit integer), i64 (64-bit integer), f32 (32-bit float), f64 (64-bit float), and v128 (128-bit SIMD vector).

8. What is the WebAssembly text format (WAT)?

   • Answer: WAT is a human-readable representation of WebAssembly code. It's useful for debugging, understanding the structure of a Wasm module, and for writing and testing small Wasm modules.

9. Explain the concept of linear memory in WebAssembly.

   • Answer: Linear memory is a contiguous block of memory accessible by a WebAssembly module. It's similar to a dynamically sized array of bytes. The module can grow or shrink this memory during runtime, but it's always a single, continuous block.

10. What is the role of the `import` and `export` statements in WebAssembly?

    • Answer: `import` statements declare functions or memory that the module needs from the host environment (usually JavaScript). `export` statements declare functions or memory that the module makes available to the host environment.

11. What is WebAssembly's garbage collection mechanism?

    • Answer: WebAssembly itself doesn't have built-in garbage collection. Memory management is typically handled by the underlying language used to compile to Wasm (e.g., Rust's ownership system or C++'s manual memory management). Future versions of WebAssembly might incorporate garbage collection.

12. How can you debug WebAssembly code?

    • Answer: Debugging can be challenging. Techniques include using browser developer tools (which have improved support for Wasm), using logging statements within the Wasm code (printed to the console via JavaScript interaction), and using debuggers for the source language (before compilation to Wasm).

13. What are some common use cases for WebAssembly?

    • Answer: Common use cases include game development, image/video processing, audio synthesis, CAD software, scientific computing, and applications requiring high performance in the browser.

14. What is the difference between `const`, `let`, and `var` in JavaScript when used with WebAssembly?

    • Answer: These keywords govern the scope and mutability of JavaScript variables, not directly within the WebAssembly module itself. How they affect interactions with WebAssembly depends on how the JavaScript code interacts with imported/exported Wasm functions and data. `const` creates read-only variables, `let` creates block-scoped variables, and `var` creates function-scoped variables.

15. Explain the concept of SIMD in WebAssembly.

    • Answer: SIMD (Single Instruction, Multiple Data) allows performing the same operation on multiple data points simultaneously, significantly boosting performance for vectorized operations like image processing. WebAssembly's `v128` type supports SIMD instructions.

16. What is the WebAssembly System Interface (WASI)?

    • Answer: WASI is a standardized API that provides a way for WebAssembly modules to interact with the operating system, independent of the underlying web browser or runtime environment. This enhances portability and allows running Wasm modules outside the browser.

17. How can you handle exceptions in WebAssembly?

    • Answer: WebAssembly has a structured exception handling mechanism using `try`, `catch`, and `finally` blocks (similar to JavaScript). Exceptions can be thrown from within Wasm code and caught by the JavaScript environment or within other Wasm functions.

18. What are some tools for compiling to WebAssembly?

    • Answer: Popular tools include Emscripten (for C/C++), Binaryen (a low-level compiler), and various compilers for Rust, Go, and other languages.

19. Describe the process of building a WebAssembly module from C++ code.

    • Answer: Typically, Emscripten is used. The process involves using Emscripten's toolchain (emcc) to compile the C++ code, generating a .wasm file, and then using JavaScript to load and instantiate the module in a web page.

20. How do you handle memory management in WebAssembly when using C++?

    • Answer: Memory management in C++ compiled to WebAssembly usually relies on manual techniques like `malloc` and `free` or smart pointers. Care must be taken to avoid memory leaks.

21. What are some performance considerations when working with WebAssembly?

    • Answer: Minimize calls between JavaScript and WebAssembly, optimize memory access patterns, use SIMD instructions where appropriate, and profile your code to identify bottlenecks.

22. Explain the concept of "Wasm modules" and how they are used.

    • Answer: A Wasm module is a self-contained unit of WebAssembly code. It contains functions, memory, tables, and other elements. It's loaded into a JavaScript environment, instantiated, and then its functions can be called from JavaScript or other Wasm modules.

23. How does WebAssembly achieve its high performance?

    • Answer: High performance comes from its binary format (fast to parse and execute), efficient instruction set, and its ability to be compiled to near-native code. The browser's Wasm runtime is optimized for execution.

24. What are some security considerations when using WebAssembly?

    • Answer: WebAssembly's sandboxed environment is inherently secure. However, vulnerabilities can arise from improper memory management (leading to buffer overflows), insecure interactions with JavaScript, and flaws in the source code being compiled to Wasm.

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