Understanding Emscripten: What it Means, How it Works, and Its Impact on WebDev

Emscripten is a cutting-edge tool that has fundamentally changed the landscape of software development in recent years. Essentially, it’s an open-source LLVM-to-JavaScript/WebAssembly compiler that has facilitated the seamless porting of native code to the web. In fact, according to its GitHub page, this LLVM-based project has been extensively used by industry giants such as Mozilla and Google, serving as the backbone for their web-based applications. In this glossary page, we will explore the definition of Emscripten, its working mechanism, the benefits of using it, and some best practices to employ when working with this tool.

“Emscripten is a powerful bridge to bring the knowledge and skill from existing languages like C and C++, and the performance of the web platform closer together.” – Brendan Eich, Creator of JavaScript

What is Emscripten? Definition of Emscripten (compiler)

Emscripten is a source-to-source compiler that converts code written in languages like C, C++, and others into JavaScript (asm.js) and WebAssembly (wasm) format. It is an open-source project currently maintained by the Mozilla Foundation. Emscripten allows developers to port their existing native applications to the web while maintaining near-native performance. This way, users can access the applications directly through a browser without the need to download or install any additional software.

ℹ️ Synonyms: Transpilation, WebAssembly, JavaScript, LLVM, Compiler, Code generation.

How it Works

The core functionality of Emscripten relies on LLVM, a widely-used compiler infrastructure. Emscripten takes LLVM bytecode generated by LLVM’s frontends for various languages (C, C++, etc.) as input and generates JavaScript or WebAssembly as output. The generated code can be run in any modern web browser that supports asm.js or WebAssembly, providing portability and access to a wide range of devices and platforms.

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Emscripten also provides a comprehensive set of libraries that simulate native system functionality, allowing developers to reuse their existing code without the need for extensive refactoring. These libraries include wrappers for popular APIs like OpenGL (WebGL), OpenAL (WebAudio), and SDL, as well as basic libc support.

Benefits of using Emscripten

  • Brings native applications to the web: Emscripten makes it possible to port existing native applications to the web with little or no modification to the source code. This allows developers to reach a broader audience by making their applications available on multiple platforms, including desktops, laptops, and mobile devices.
  • Near-native performance: Emscripten-generated code targets asm.js and WebAssembly, both of which provide near-native execution speed. This enables developers to deliver high-performance web applications, even for computationally intensive tasks.
  • Reusable code: Emscripten provides libraries that mimic popular native APIs, allowing developers to reuse their existing codebase without major refactoring or reimplementation. This can save significant time and resources compared to rewriting the application from scratch for the web.
  • Wide platform support: Emscripten-generated code runs on any modern web browser that supports asm.js or WebAssembly, providing extensive reach to a variety of devices and operating systems.
  • Part of the vibrant web ecosystem: By using Emscripten, developers can benefit from web-specific technologies and tools like browser-based debugging, browser performance profilers, and web development frameworks.

Emscripten use cases

Emscripten has been used to port a wide range of native applications to the web, including:

Popular programming languages:

Languages like Python, Lua, and Ruby have been ported using Emscripten, allowing these languages to run directly in the browser.

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Games and game engines:

Several popular games and game engines have been successfully ported using Emscripten, such as Unity, Unreal Engine, and classic games like DOOM.

Scientific simulations and visualization:

Emscripten has been used to bring powerful scientific simulation tools and visualization applications like ParaView and VTK to the web.

Desktop applications:

Projects like AutoCAD and Figma have leveraged Emscripten to provide fully-featured, browser-based alternatives to their native desktop applications.

Best Practices

When working with Emscripten, it’s essential to keep in mind a few key practices to achieve optimal results. Start by targeting smaller, modular parts of your application for porting rather than the entire codebase. This will make it easier to manage the porting process and identify potential issues. Keep your codebase up-to-date with the latest Emscripten versions for better support and performance improvements. Use Emscripten’s profiling and optimization tools to identify bottlenecks and improve the performance of the ported application. Finally, consult Emscripten’s extensive documentation and community resources to better understand the process and overcome any challenges.

Most recommended books about Emscripten

For those eager to dive deeper into Emscripten, the following resources are highly recommended:

Emscripten: An LLVM-to-JavaScript Compiler

By: Alon Zakai
This book, authored by the creator of Emscripten, serves as a comprehensive introduction to the tool, its purpose, and syntax.

WebAssembly in Action

By: Gerard Gallant
While not exclusively about Emscripten, this book provides an in-depth understanding of WebAssembly and how it can be used in conjunction with tools like Emscripten to create performant web applications.


In summary, Emscripten is a powerful tool for porting native applications to the web, enabling developers to reach a broader audience and take advantage of the extensive capabilities of modern browsers. With its extensive libraries, near-native performance, and wide platform support, Emscripten has become an essential part of the software development toolkit for many organizations and projects.

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Back in 2013, I founded Echo with the simple business idea: "Connect great tech companies around the globe with the brightest software engineers in Eastern Europe." We've employed hundreds of talents so far and keep going.
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li-url Lou Reverchuk

IT Entrepreneur

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