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WEBASSEMBLY LEARNING PROJECTS

Understanding WebAssembly Deeply

To truly understand WebAssembly, you need to grapple with its stack-based virtual machine, linear memory model, binary format, and host environment interaction. This guide breaks down WebAssembly into its core concepts and provides projects that force you to confront each of them.

Core Concept Analysis

WebAssembly breaks down into these fundamental building blocks:

Concept What It Means
Stack Machine Operations push/pop values from a virtual stack—no registers
Linear Memory A flat, contiguous byte array that WASM modules can grow
Binary Format Compact .wasm bytecode with specific section structure
Text Format (WAT) Human-readable S-expression syntax that compiles to WASM
Module System Imports, exports, functions, tables, globals, memory
Type System Only 4 numeric types: i32, i64, f32, f64 (plus reference types)
Host Binding How WASM talks to JavaScript, WASI, or other hosts
Sandboxing Memory isolation, no direct system access

Project 1: Hand-Write WAT Programs

  • File: WEBASSEMBLY_LEARNING_PROJECTS.md
  • Programming Language: WAT (WebAssembly Text Format)
  • Coolness Level: Level 4: Hardcore Tech Flex
  • Business Potential: 1. The “Resume Gold”
  • Difficulty: Level 2: Intermediate
  • Knowledge Area: Low-Level Web / Compilers
  • Software or Tool: WebAssembly
  • Main Book: “WebAssembly: The Definitive Guide” by Brian Sletten

What you’ll build: A collection of programs written directly in WebAssembly Text Format (WAT) that you assemble and run—covering arithmetic, control flow, memory operations, and function calls.

Why it teaches WebAssembly: Writing WAT by hand forces you to think in stack operations. You’ll feel the constraint of “no variables, only stack” and understand why WASM is designed the way it is. You’ll see exactly what high-level compilers produce.

Core challenges you’ll face:

  • Understanding stack discipline (challenge maps to: stack machine model)
  • Managing local variables vs. stack values (maps to: WASM execution model)
  • Implementing loops and conditionals with structured control flow (maps to: block/loop/if constructs)
  • Reading and writing linear memory manually (maps to: memory model)
  • Calling imported functions from the host (maps to: host binding)

Resources for key challenges:

  • “WebAssembly Specification” - The official spec’s text format section is surprisingly readable
  • “Understanding WebAssembly text format” on MDN - Excellent hands-on tutorial

Key Concepts:

  • Stack-based execution: MDN WebAssembly Concepts - Mozilla
  • WAT syntax: “Understanding WebAssembly text format” - MDN Web Docs
  • Control flow in WASM: WebAssembly Specification §4.4 - W3C

Difficulty: Beginner Time estimate: Weekend Prerequisites: Basic programming, understanding of assembly concepts helpful

Real world outcome: You’ll have working programs that run in the browser or Node.js. For example: a WAT program that calculates Fibonacci numbers, which you can call from JavaScript and see the result in the console. You’ll also build a simple memory-based string reverser where you watch bytes move in memory.

Learning milestones:

  1. First WAT function compiles and runs → you understand stack push/pop
  2. Implement a loop with memory access → you understand linear memory addressing
  3. Import a JS function and call it from WAT → you understand the host boundary

Project 2: Build a WASM Binary Parser

  • File: WEBASSEMBLY_LEARNING_PROJECTS.md
  • Main Programming Language: C
  • Alternative Programming Languages: Rust, Python, TypeScript
  • Coolness Level: Level 4: Hardcore Tech Flex
  • Business Potential: Level 1: The “Resume Gold”
  • Difficulty: Level 2: Intermediate (The Developer)
  • Knowledge Area: WebAssembly, Binary Parsing
  • Software or Tool: WebAssembly
  • Main Book: WebAssembly Specification (W3C)

What you’ll build: A program (in C, Rust, or Python) that reads .wasm binary files and prints their structure—sections, function types, imports, exports, code.

Why it teaches WebAssembly: The binary format IS WebAssembly. By parsing it byte-by-byte, you’ll understand exactly how modules are structured, how LEB128 encoding works, and what information the runtime needs to execute code.

Core challenges you’ll face:

  • Parsing LEB128 variable-length integers (maps to: WASM encoding)
  • Understanding section IDs and their ordering (maps to: module structure)
  • Decoding function signatures and type indices (maps to: type system)
  • Parsing the code section’s instruction opcodes (maps to: instruction set)
  • Handling the binary format’s compactness vs. readability tradeoffs (maps to: design decisions)

Resources for key challenges:

  • “WebAssembly Binary Format” specification - The definitive reference for byte-level structure
  • “Writing a WASM Runtime” series by Syrus Akbary - Practical walkthrough of parsing

Key Concepts:

  • LEB128 encoding: WebAssembly Specification §5.2 - W3C
  • Module sections: “WebAssembly Module Structure” - WebAssembly.org
  • Binary opcodes: WebAssembly Specification §5.4 (Instructions) - W3C

Difficulty: Intermediate Time estimate: 1-2 weeks Prerequisites: Comfortable with binary/hex, file I/O, basic data structures

Real world outcome: Run your parser on any .wasm file and get human-readable output like:

Section: Type (1)
  func [i32, i32] -> [i32]
Section: Function (3)
  func 0: type 0
Section: Export (7)
  "add" -> func 0
Section: Code (10)
  func 0: local.get 0, local.get 1, i32.add, end

Learning milestones:

  1. Parse the magic number and version → you understand WASM file identity
  2. Decode all section types → you understand module anatomy
  3. Disassemble the code section → you can read raw WASM bytecode

Project 3: Build a WASM Interpreter

  • File: WEBASSEMBLY_LEARNING_PROJECTS.md
  • Main Programming Language: C
  • Alternative Programming Languages: Rust, Go, TypeScript
  • Coolness Level: Level 5: Pure Magic (Super Cool)
  • Business Potential: Level 1: The “Resume Gold”
  • Difficulty: Level 3: Advanced (The Engineer)
  • Knowledge Area: WebAssembly, Virtual Machines
  • Software or Tool: WebAssembly, wasmtime
  • Main Book: Computer Systems: A Programmer’s Perspective by Bryant & O’Hallaron

What you’ll build: A working interpreter that executes WebAssembly bytecode—implementing the stack machine, memory, and basic instruction set.

Why it teaches WebAssembly: This is the deepest understanding possible. You’ll implement i32.add, local.get, call, br_if, memory load/store—everything. When you’re done, you’ll know WASM like you designed it.

Core challenges you’ll face:

  • Implementing a value stack with type safety (maps to: stack machine semantics)
  • Managing call frames and local variables (maps to: function execution)
  • Implementing structured control flow (block, loop, br, br_if) (maps to: WASM’s unique control flow)
  • Linear memory with bounds checking (maps to: memory safety model)
  • Import/export resolution (maps to: module linking)

Resources for key challenges:

  • “Writing a WebAssembly Interpreter” by Colin Eberhardt - Step-by-step in TypeScript
  • “Computer Systems: A Programmer’s Perspective” by Bryant & O’Hallaron (Ch. 3) - Understanding machine-level execution
  • WebAssembly Specification §4 (Execution) - The formal semantics

Key Concepts:

  • Stack machine execution: WebAssembly Specification §4.4 - W3C
  • Structured control flow: “WebAssembly’s Structured Control Flow” - Mozilla Hacks
  • Memory model: “Linear Memory” - WebAssembly.org documentation
  • Validation: WebAssembly Specification §3 (Validation) - W3C

Difficulty: Advanced Time estimate: 1 month+ Prerequisites: Strong programming skills, completed Project 2 (parser)

Real world outcome: Your interpreter runs real .wasm files. You can execute the official WebAssembly test suite and watch your interpreter pass hundreds of conformance tests. You’ll be able to run compiled C/Rust programs through your own execution engine.

Learning milestones:

  1. Execute arithmetic instructions → you understand the value stack
  2. Implement function calls → you understand activation records in WASM
  3. Implement br and br_if correctly → you understand WASM’s unique control flow model
  4. Pass the official test suite → you have a conformant implementation

Project 4: Compile a Language to WASM

  • File: WEBASSEMBLY_LEARNING_PROJECTS.md
  • Main Programming Language: C
  • Alternative Programming Languages: Rust, Go, TypeScript
  • Coolness Level: Level 5: Pure Magic (Super Cool)
  • Business Potential: Level 5: The “Industry Disruptor”
  • Difficulty: Level 4: Expert (The Systems Architect)
  • Knowledge Area: Compilers, WebAssembly
  • Software or Tool: WebAssembly, LLVM
  • Main Book: Engineering a Compiler by Cooper & Torczon

What you’ll build: A compiler for a simple language (arithmetic expressions, variables, functions, control flow) that outputs .wasm binary files.

Why it teaches WebAssembly: Compilation forces you to understand WASM as a target. You’ll see why certain design decisions were made—why structured control flow instead of goto, why a stack machine, why only 4 numeric types.

Core challenges you’ll face:

  • Generating LEB128-encoded binary output (maps to: binary format mastery)
  • Stack allocation for expression evaluation (maps to: stack machine code generation)
  • Implementing variables as locals vs. memory (maps to: storage model decisions)
  • Compiling control flow to WASM blocks (maps to: structured control flow)
  • Type checking matching WASM’s type system (maps to: WASM type constraints)

Resources for key challenges:

  • “Writing a C Compiler” by Nora Sandler - Compiler fundamentals (adapt target to WASM)
  • “Compiling to WebAssembly” by Syrus Akbary - WASM-specific codegen strategies
  • “Engineering a Compiler” by Cooper & Torczon (Ch. 7) - Code generation theory

Key Concepts:

  • Code generation for stack machines: “Engineering a Compiler” Ch. 7 - Cooper & Torczon
  • WASM binary encoding: WebAssembly Specification §5 - W3C
  • Type-directed compilation: “Writing a C Compiler” - Nora Sandler

Difficulty: Advanced Time estimate: 1 month+ Prerequisites: Basic compiler knowledge, completed Projects 1 and 2

Real world outcome: Write programs in your language, compile them to .wasm, and run them in a browser or with wasmtime. For example:

func fib(n) {
  if n < 2 { return n }
  return fib(n-1) + fib(n-2)
}

Compiles to valid WASM that you can call from JavaScript.

Learning milestones:

  1. Compile arithmetic expressions → you understand stack-based codegen
  2. Compile functions with locals → you understand WASM function structure
  3. Compile if/while to blocks → you deeply understand WASM control flow
  4. Self-host or bootstrap → ultimate understanding

Project 5: Build a WASI Runtime

  • File: WEBASSEMBLY_LEARNING_PROJECTS.md
  • Main Programming Language: C
  • Alternative Programming Languages: Rust, Go, Zig
  • Coolness Level: Level 5: Pure Magic (Super Cool)
  • Business Potential: Level 4: The “Open Core” Infrastructure
  • Difficulty: Level 3: Advanced (The Engineer)
  • Knowledge Area: WebAssembly, System Interfaces
  • Software or Tool: WASI, wasmtime
  • Main Book: WebAssembly Specification (W3C)

What you’ll build: An extension to your interpreter (Project 3) that implements WASI—the WebAssembly System Interface—allowing WASM programs to do file I/O, read environment variables, and more.

Why it teaches WebAssembly: WASI shows how WASM escapes the browser sandbox while maintaining security. You’ll understand capability-based security, how imports become system calls, and why WASM is becoming a universal runtime.

Core challenges you’ll face:

  • Implementing file descriptors and preopens (maps to: capability-based security)
  • Memory marshalling for syscalls (maps to: host/guest data transfer)
  • Implementing fd_read, fd_write, path_open (maps to: POSIX-like abstraction)
  • Argument and environment passing (maps to: program initialization)

Resources for key challenges:

  • WASI Specification on GitHub - The canonical reference
  • “Standardizing WASI” by Lin Clark - Excellent illustrated explanation
  • Wasmtime source code - Reference implementation to study

Key Concepts:

  • Capability-based security: “What is WASI?” - Bytecode Alliance blog
  • WASI API surface: WASI Specification - GitHub/WebAssembly/WASI
  • Host function imports: WebAssembly Specification §4.5 - W3C

Difficulty: Advanced Time estimate: 2-3 weeks (after Project 3) Prerequisites: Completed Project 3, familiarity with POSIX syscalls

Real world outcome: Run command-line WASM programs compiled with clang --target=wasm32-wasi:

$ ./your-runtime hello.wasm
Hello from WebAssembly!
$ ./your-runtime cat.wasm /etc/hostname
mycomputer

Learning milestones:

  1. Implement fd_write to stdout → programs can print
  2. Implement fd_read from stdin → programs can read input
  3. Implement filesystem access with preopens → you understand capability model

Project Comparison Table

Project Difficulty Time Depth of Understanding Fun Factor
Hand-Write WAT Beginner Weekend ⭐⭐⭐ (foundational) ⭐⭐⭐⭐
WASM Binary Parser Intermediate 1-2 weeks ⭐⭐⭐⭐ (structural) ⭐⭐⭐
WASM Interpreter Advanced 1 month+ ⭐⭐⭐⭐⭐ (complete) ⭐⭐⭐⭐⭐
Compile to WASM Advanced 1 month+ ⭐⭐⭐⭐⭐ (production view) ⭐⭐⭐⭐
WASI Runtime Advanced 2-3 weeks ⭐⭐⭐⭐ (systems integration) ⭐⭐⭐⭐

Recommendation

Based on wanting to deeply understand WebAssembly:

Start with Project 1 (Hand-Write WAT) this weekend. It costs almost nothing but gives you the mental model everything else builds on. You’ll understand the stack machine in your bones.

Then build Project 2 (Binary Parser) over the next 1-2 weeks. This demystifies the .wasm format completely.

Finally, tackle Project 3 (Interpreter) for the deepest possible understanding. When you’ve implemented br_if and watched your stack machine execute a loop, you’ll understand WebAssembly at a level few developers ever reach.

Final Capstone Project: Full-Stack WASM Toolchain

What you’ll build: A complete WebAssembly toolchain—a simple language, its compiler to WASM, a binary validator, an interpreter with WASI support, and a simple debugger that can step through WASM execution.

Why it teaches WebAssembly: You’ll have touched every layer: authoring (WAT/language), compilation (codegen), validation (type checking), execution (interpreter), and systems integration (WASI). This is how the WebAssembly ecosystem actually works.

Core challenges you’ll face:

  • Integrating all previous projects into a cohesive toolchain
  • Implementing validation per the spec (reject malformed modules)
  • Building a debugger that shows stack state and memory
  • Supporting multiple output targets (browser JS glue, WASI CLI)
  • Optimizations (constant folding, dead code elimination)

Key Concepts:

  • Toolchain architecture: “LLVM: A Compilation Framework” - Chris Lattner
  • WASM validation: WebAssembly Specification §3 - W3C
  • Debugging VMs: “Building a Debugger” - Sy Brand

Difficulty: Expert Time estimate: 2-3 months Prerequisites: Completed Projects 1-4

Real world outcome: A working toolchain you can demo:

$ ./mywasmcc factorial.mylang -o factorial.wasm
$ ./mywasm validate factorial.wasm
Valid module: 1 function, 0 imports, 1 export
$ ./mywasm run factorial.wasm --arg 10
3628800
$ ./mywasm debug factorial.wasm
(wdb) break factorial
(wdb) run --arg 5
Breakpoint hit at factorial
(wdb) stack
[i32: 5]
(wdb) step
...

Learning milestones:

  1. Compiler produces valid WASM → end-to-end works
  2. Interpreter passes conformance tests → spec-compliant
  3. Debugger shows execution state → you can teach others
  4. Someone else uses your toolchain → production quality

Additional Resources

Official Documentation

Books

  • “WebAssembly: The Definitive Guide” by Brian Sletten - O’Reilly
  • “Programming WebAssembly with Rust” by Kevin Hoffman - Pragmatic Bookshelf

Tools

  • wabt - WebAssembly Binary Toolkit (wat2wasm, wasm2wat, etc.)
  • wasmtime - Fast WASI runtime
  • wasm3 - High-performance interpreter (good reference)

This progression takes you from “I know WebAssembly exists” to “I could implement a WASM runtime from scratch.”