C/C++ Runtime for Web Assembly

Version 2.0.0

tiny-wasm-runtime is a simple, lightweight and easy to use C/C++ library for building Web Assembly code directly with clang. It solves some common use cases with less work than the more feature rich emscripten. tiny-wasm-runtime is easy to understand, and has some cool features. You can input and print streaming character i/o to a <div> tag, use a <canvas> element as an ANSI terminal, or use a C/C++ 2D drawing api (that is compatible with JavaScript Canvas APIs) to draw to a <canvas> element. You can run blocking C/C++.

tiny-wasm-runtime allows you to run C/C++ code in a web browser. Legacy code, libraries, full applications, or single functions can be integrated with JavaScript and Typescript.

tiny-wasm-runtime is designed to be used with the standard llvm clang compiler and tools.

C++ Bouncing Balls Demo

View bouncing balls here

Key Features

  • compile C/C++ for use with web assembly using clang directly
  • standard C library, libc++. and purpose built APIs
  • Localization support, UTF-8, and windows-1252 support
  • load web assembly modules, and call their C/C++ functions from JavaScript (with parameter conversion as needed)
  • in C/C++, printf and get characters to/from <div> tags in your HTML page
  • in C/C++, printf and get characters to/from a <canvas> based "terminal"
  • in C/C++ use 2D drawing API compatible with JavaScript Canvas
  • in C/C++, use the "blocking loop" pattern and integrate with JavaScript's asynchronous event loop


The Wasm Problem section explains why a C/C++ Runtime is needed for Web Assembly.

Hello World

Here is the simplest tiny-wasm-runtime example.

C code:

   #include <stdio.h>

   void hello() {
      printf("hello world\n");


    <title>Hello World</title>
    <div id="twr_iodiv"></div>

    <script type="module">
        import {twrWasmModule} from "tiny-wasm-runtime";

        const mod = new twrWasmModule();
        await mod.loadWasm("./helloworld.wasm");
        await mod.callC(["hello"]);

View Live Demos

Name View Live Link Source Link
Bouncing Balls (C++) View bouncing balls Source for balls
Maze (Win32 C Port) View live maze Source for maze
Input from <div> View square demo Source
Mini-Terminal from <canvas> View mini-term demo Source

On Github


Version 2.0 vs. 1.0

  • libc++ for wasm/clang is now available
  • most of the standard C library is now implemented
  • instructions for source level debugging
  • version of library with debug symbols provided
  • locale, UTF-8, and windows-1252 support

Version 2.0.0 Limitations

  • libc++ not built with threads, rtti, exceptions, unicode, or wide char support
  • some standard C library functions are not 100% implemented
  • Designed to work with a browser. Not tested with or designed to work with node.js
  • Not all of compile-rt is ported (but most bits you need are)
  • The following non-compatible changes since 1.0 (relatively minor)
    • there is no longer 'twr_' prefixed std c lib functions (use the normal std c lib names)
    • most 'twr_wasm_' prefixed functions have been shortened to 'twr_'.
    • some functions were renamed or changed slightly to be more consistent, but no functionality is lost.

Post Feedback

Please post feedback (it worked for you, didn't work, requests, questions, etc) at https://github.com/twiddlingbits/tiny-wasm-runtime/