Hiring guide for WebAssembly Engineers

WebAssembly Developer Hiring Guide

WebAssembly, often abbreviated as WASM, is a binary instruction format designed as a portable target for the compilation of high-level languages like C++, enabling deployment on the web for client and server applications. It was first announced in 2015 by W3C with major contributions from Mozilla, Microsoft, Google and Apple. Unlike JavaScript, WebAssembly is not primarily intended to be written or edited by humans but rather generated from source code using compilers. Its compact binary format allows it to load faster than equivalent software written in other languages meant for browsers. As per its design goal stated by W3C: "WebAssembly enables near-native performance" thus making it an essential tool in modern web development.

Ask the right questions secure the right WebAssembly talent among an increasingly shrinking pool of talent.

First 20 minutes

General WebAssembly app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in WebAssembly application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you describe the role of WebAssembly in web development?
WebAssembly is a binary instruction format that serves as a compile target for high-level languages like C, C++, and Rust. It enables developers to run code on the web at near-native speed, which is critical for performance-intensive applications like games, computer-aided design, video editing, and more.
What are the benefits of using WebAssembly?
WebAssembly offers several benefits including faster parsing time compared to JavaScript, efficient execution and compact binary format. It also provides a secure sandbox execution environment and is designed to be a low-level virtual machine that runs code at near-native speed.
Describe the difference between JavaScript and WebAssembly.
While both JavaScript and WebAssembly can be used for browser-based applications, they differ in several ways. JavaScript is a high-level programming language, while WebAssembly is a low-level binary format. WebAssembly offers faster parsing and execution than JavaScript, which can be crucial for performance-intensive applications.
Can you explain how WebAssembly interacts with JavaScript?
WebAssembly and JavaScript can interact in a symbiotic way. WebAssembly modules are loaded into a JavaScript environment where they can be instantiated and interacted with via JavaScript. JavaScript can call WebAssembly functions, and WebAssembly can call JavaScript functions as well.
How would you compile a C/C++ code to WebAssembly?
To compile a C/C++ code to WebAssembly, we can use Emscripten, which is a toolchain for compiling to asm.js and WebAssembly. The command 'emcc helloworld.c -s WASM=1 -o helloworld.html' would compile a C file named 'helloworld.c' into a WebAssembly module.
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What you’re looking for early on

Does the candidate have a solid understanding of WebAssembly?
Has the candidate demonstrated experience with JavaScript and other relevant programming languages?
Is the candidate able to explain complex technical concepts in simple terms?
Can the candidate solve complex problems and debug issues effectively?

Next 20 minutes

Specific WebAssembly development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What are the limitations of WebAssembly?
WebAssembly can't directly access the DOM or other web APIs; it must go through JavaScript for that. Also, its multithreading support is still experimental, and it doesn't have garbage collection built in, which makes it less suitable for languages that require it.
How do you debug a WebAssembly module?
Debugging WebAssembly can be done using browser developer tools. Most modern browsers support source maps for WebAssembly, which allows developers to debug their code at the source level. Also, Emscripten provides options to generate source maps for the compiled WebAssembly module.
How does WebAssembly handle memory management?
WebAssembly uses a linear memory model. It exposes memory to the developer as a resizable array buffer. Any resizing operation either from JavaScript or WebAssembly code updates the buffer, and it's the developer's responsibility to perform memory management within this model.
How would you optimize a WebAssembly application?
WebAssembly application can be optimized by reducing the size of the WebAssembly binary, optimizing the use of memory, and using WebAssembly's structured control flow. Also, choosing the right compilation target and using efficient algorithms and data structures can help optimize a WebAssembly application.
What is the role of the WebAssembly text format (WAT)?
The WebAssembly text format (WAT) is a representation of WebAssembly binary code in a human-readable form. It's useful for debugging, understanding the performance aspects of your code, and for educational purposes to understand how WebAssembly works.
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The ideal back-end app developer

What you’re looking to see on the WebAssembly engineer at this point.

At this point, a skilled WebAssembly engineer should demonstrate strong problem-solving abilities, proficiency in WebAssembly programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with WebAssembly.

What does the following WebAssembly code do?
  (func (export "add") (param i32 i32) (result i32)
    get_local 0
    get_local 1
This code defines a WebAssembly module with a single function named 'add'. The function takes two 32-bit integers as parameters and returns their sum.
What will be the output of the following WebAssembly code?
  (func $calculate (param $p1 i32) (param $p2 i32) (result i32)
    get_local $p1
    get_local $p2
  (export "calculate" (func $calculate)))
This code doesn't output anything by itself. It defines a WebAssembly module with a function 'calculate' that multiplies two 32-bit integers. The function can be called from JavaScript with two parameters, and it will return their product.
What does the following WebAssembly code do with the memory array?
  (memory 1)
  (func (export "init")
    i32.const 0
    i32.const 42
This code defines a WebAssembly module with a single page of memory and a function named 'init'. The function stores the 32-bit integer 42 at the zeroth index of the memory array.
What does the following WebAssembly code do related to threading?
  (memory 1)
  (func (export "store") (param i32)
    get_local 0
    i32.const 0
  (func (export "load") (result i32)
    i32.const 0
This code defines a WebAssembly module with a single page of memory and two functions: 'store' and 'load'. The 'store' function takes a 32-bit integer as a parameter and stores it at the zeroth index of the memory array. The 'load' function returns the 32-bit integer stored at the zeroth index of the memory array. This module can be used to share data between WebAssembly threads.

Wrap-up questions

Final candidate for WebAssembly Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle WebAssembly application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

Describe how WebAssembly ensures security.
WebAssembly is designed with a strong focus on security. It runs inside a sandboxed environment and has no direct access to the underlying system. It uses a validated, structured control flow to prevent common vulnerabilities like buffer overflows, and all its operations are defined in a way that allows them to be efficiently sandboxed.
How would you integrate a WebAssembly module into a React application?
To integrate a WebAssembly module into a React application, you would first compile your source code (C, C++, Rust, etc.) into a WebAssembly module. Then, you'd use the WebAssembly JavaScript API to load and instantiate this module inside your React component, and use the exported functions as needed.
What is the role of Emscripten in WebAssembly development?
Emscripten is a toolchain that compiles C and C++ code into WebAssembly. It provides a complete set of libraries and allows developers to port their C and C++ applications to the web. Emscripten also generates the necessary JavaScript 'glue' code that integrates the WebAssembly module into a web environment.

WebAssembly application related

Product Perfect's WebAssembly development capabilities

Beyond hiring for your WebAssembly engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in WebAssembly projects, and can engage in multiple capacities.