Book Image

Practical WebAssembly

By : Sendil Kumar Nellaiyapen
Book Image

Practical WebAssembly

By: Sendil Kumar Nellaiyapen

Overview of this book

Rust is an open source language tuned toward safety, concurrency, and performance. WebAssembly brings all the capabilities of the native world into the JavaScript world. Together, Rust and WebAssembly provide a way to create robust and performant web applications. They help make your web applications blazingly fast and have small binaries. Developers working with JavaScript will be able to put their knowledge to work with this practical guide to developing faster and maintainable code. Complete with step-by-step explanations of essential concepts, examples, and self-assessment questions, you’ll begin by exploring WebAssembly, using the various tools provided by the ecosystem, and understanding how to use WebAssembly and JavaScript together to build a high-performing application. You’ll then learn binary code to work with a variety of tools that help you to convert native code into WebAssembly. The book will introduce you to the world of Rust and the ecosystem that makes it easy to build/ship WebAssembly-based applications. By the end of this WebAssembly Rust book, you’ll be able to create and ship your own WebAssembly applications using Rust and JavaScript, understand how to debug, and use the right tools to optimize and deliver high-performing applications.
Table of Contents (15 chapters)
Section 1: Introduction to WebAssembly
Section 2: WebAssembly Tools
Section 3: Rust and WebAssembly

Generating asm.js using Emscripten

We will use Emscripten to port C/C++ programs into asm.js or the WebAssembly binary and then run them inside the JavaScript engine.


Programming languages such as Lua and Python have a C/C++ runtime. With Emscripten, we can port the runtime as a WebAssembly module and execute them inside the JavaScript engine. This makes it easy to run Lua/Python code on the JavaScript engine. Thus, Emscripten and WebAssembly allow the running of native code in the JavaScript engine.

First, let's create a sum.cpp file:

 // sum.cpp
extern "C" {
  unsigned sum(unsigned a, unsigned b) {
      return a + b;

Consider extern "C" as something like an export mechanism. All the functions inside are available as an exported function without any changes to their name. Then, we define the normal sum function that takes in two numbers and returns a number.

In order to generate...