1.0.1 • Public • Published

Tiny Web Assembly Runtime

tiny-wasm-runtime is a simple, lightweight and easy to use C/C++ runtime for Web Assembly. 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 character i/o to <div> and <canvas> elements, run blocking C/C++, and use Javascript <canvas> 2D drawing apis.

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.

View the Bouncing Ball Demo

Click Here to view demo using tiny-wasm-runtime and it's C/C++ Canvas APIs

Key Features

  • 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
  • linked with helloworld, code+data < 3K


Clone from github, or use npm install tiny-wasm-runtime. To compile C/C++, install clang and wasm-ld.

Full Documentation

The full documentation can be found here

Live Demos

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

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"]);

Simple <div> i/o

I/O can be directed to or from a <div> or a <canvas> tag. Here is a simple example using a <div> for stdio input and output.

#include <stdio.h>
#include <stdlib.h>
#include "twr-crt.h"

void stdio_div() {
    char inbuf[64];
    int i;

    printf("Square Calculator\n");

    while (1) {
        printf("Enter an integer: ");
        printf("%d squared is %d\n\n",i,i*i);

With an index.html like the following. This time we are using twrWasmModuleAsync which integrates blocking C code into Javascript. twrWasmModuleAsync can also be used to receive key input from a <div> or <canvas> tag.

	<title>stdio-div example</title>
	<div id="twr_iodiv" style="background-color:LightGray;color:DarkGreen" tabindex="0">Loading... <br></div>

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

		let amod;
		try {
			amod = new twrWasmModuleAsync();

			document.getElementById("twr_iodiv").innerHTML ="<br>";

			await amod.loadWasm("./stdio-div.wasm");
			await amod.callC(["stdio_div"]);
		catch(ex) {
			amod.divLog("unexpected exception");
			throw ex;


Full Documentation

The full documentation can be found here

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npm i tiny-wasm-runtime

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  • twiddlingbits