WebAssembly Interview Questions and Answers for 2 years experience

1. What is WebAssembly?

   • Answer: WebAssembly (Wasm) is a binary instruction format for a stack-based virtual machine. It's designed as a portable target for compilation of high-level languages like C, C++, Rust, and Go, enabling them to run in web browsers at near-native speed. It's designed for performance and efficiency, complementing JavaScript rather than replacing it entirely.

2. What are the key benefits of using WebAssembly?

   • Answer: Key benefits include significantly improved performance compared to JavaScript for computationally intensive tasks, better security due to its sandboxed environment, and the ability to reuse existing codebases written in languages other than JavaScript.

3. Explain the difference between WebAssembly and JavaScript.

   • Answer: WebAssembly is a compiled, low-level binary format, while JavaScript is an interpreted, high-level language. Wasm excels at performance for computationally heavy tasks, whereas JavaScript offers better dynamic features and ease of development for many applications. They are often used together, with Wasm handling performance-critical parts and JavaScript managing the user interface and interactions.

4. How does WebAssembly interact with JavaScript?

   • Answer: WebAssembly modules expose functions to JavaScript via a JavaScript API. JavaScript can call these functions and pass data, and Wasm can, in turn, call back into JavaScript. This allows for seamless integration between the two.

5. What are the different WebAssembly module types?

   • Answer: Primarily, there's only one type: a WebAssembly module. However, within that module, you can have different function types (defined by their parameter and return types) and various data types (integers, floats, etc.).

6. Explain the WebAssembly memory model.

   • Answer: WebAssembly uses a linear memory model, which is a contiguous array of bytes. This memory is shared between the Wasm module and the JavaScript environment, allowing for data exchange. It's managed using typed arrays in JavaScript for efficient access.

7. What are WebAssembly tables?

   • Answer: WebAssembly tables are arrays of function references. They're used for indirect function calls, allowing dynamic dispatch of functions based on an index into the table. This is crucial for features like polymorphism.

8. Describe the WebAssembly global variables.

   • Answer: Global variables in WebAssembly are variables that have global scope within the module. They can be mutable or immutable, and their values can be accessed and modified (if mutable) by the Wasm code.

9. What are the different data types supported by WebAssembly?

   • Answer: WebAssembly supports various integer types (e.g., i32, i64), floating-point types (f32, f64), and optionally, references (to other WebAssembly objects).

10. How do you handle exceptions in WebAssembly?

    • Answer: WebAssembly uses traps to handle exceptions. A trap is an abrupt termination of execution due to an error (e.g., division by zero, out-of-bounds memory access). JavaScript can catch these traps using try...catch blocks when interacting with the Wasm module.

11. How to import and export functions in WebAssembly?

    • Answer: You define import and export sections in the WebAssembly module's textual representation (.wat) or binary representation (.wasm). The import section specifies functions to import from the JavaScript environment, while the export section defines functions that are accessible from JavaScript.

12. What are the different ways to compile code to WebAssembly?

    • Answer: Several compilers support WebAssembly as a target, including Emscripten (for C/C++), the Rust compiler, and various Go compilers. These tools take source code in the respective languages and generate .wasm files.

13. Explain the concept of WebAssembly threads.

    • Answer: WebAssembly's multi-threading capabilities (using threads) are a relatively recent addition. They allow for parallel execution of code within a Wasm module, which can improve performance for tasks that benefit from parallelism.

14. What are the security implications of using WebAssembly?

    • Answer: WebAssembly's sandboxed nature contributes to enhanced security. However, vulnerabilities can still exist within the Wasm code itself or in the interaction between Wasm and JavaScript. Careful code review and secure coding practices are vital.

15. How can you debug WebAssembly code?

    • Answer: Debugging can involve using browser developer tools, which sometimes offer limited Wasm debugging capabilities. More advanced techniques involve using source maps (if generated during compilation) to map Wasm instructions back to the original source code for easier debugging.

16. What are some common use cases for WebAssembly?

    • Answer: Common uses include game development, video and image processing, scientific computing, CAD software, and virtual/augmented reality applications – areas where performance is critical.

17. Describe the difference between .wat and .wasm files.

    • Answer: .wat (WebAssembly text) is a human-readable text format for WebAssembly modules. .wasm (WebAssembly binary) is the compact binary format used for execution. Compilers typically generate .wasm files from .wat or directly from source code.

18. What is the role of the WebAssembly specification?

    • Answer: The WebAssembly specification defines the precise behavior of the WebAssembly virtual machine and its instruction set. It ensures interoperability across different browsers and implementations.

19. How does garbage collection work in WebAssembly?

    • Answer: Core WebAssembly doesn't have built-in garbage collection. However, proposals for garbage collection are under development and may be included in future versions. Currently, memory management is typically handled manually or through the language's runtime environment if using languages with GC support.

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