一个单文件的 WebAssembly html 演示

Question

我在哪里可以找到一个最简单的单文件演示，显示在 html 中使用 WebAssembly？

JavaScript 示例很简单：

<script>
function hw() { console.log("Hello, world."); }
</script>
<button onclick="hw()">HW</button>

有类似 WebAssembly 的吗？

我希望它具有类似于硬编码字节缓冲区的东西，带有一个 wasm 二进制文件，它被加载并执行它的一些微不足道的功能。以下是我期望的概要：

<script>
function hw() { 
    var wasm_code = [255, 0, 128, ..., whatever, ...];
    var magic = give_me_wasm(wasm_code);
    var x = magic.my_add(2,2);
    console.log("2 + 2 = ", x); 
}
</script>
<button onclick="hw()">HW</button>

这样的demo可以做吗，一个简单的表格，可以粘贴到开发者控制台中试一试，不需要设置任何框架和工具？

Answer 1

自己做的：

<script>
var wasm_base64;
var wasm_buffer;
var wasm;
var wasm_instance;
function hw() {
    wasm_base64 = "AGFzbQEAAAABBwFgAnx8AXwDAgEABwoBBm15X2FkZAAACgkBBwAgACABoAs=";
    wasm_buffer = Uint8Array.from(atob(wasm_base64), c => c.charCodeAt(0)).buffer;
    WebAssembly.compile(wasm_buffer).then(x => {
        wasm = x;
        wasm_instance = new WebAssembly.Instance(wasm);
        var x = wasm_instance.exports.my_add(2,2);
        console.log("2+2 = ",x);
    });
}
</script>
<button onclick="hw()">HW</button>

这是嵌入的 WebAssembly 文本表单 (q.wat)：

(module
  (type (;0;) (func (param f64 f64) (result f64)))
  (func $myadd (type 0) (param f64 f64) (result f64)
    get_local 0
    get_local 1
    f64.add)
  (export "my_add" (func $myadd))
)

以下是生成 base64 缓冲区的命令行：

$ wat2wasm q.wat -o w.wasm
$ base64 -w0 w.wasm ;echo
AGFzbQEAAAABBwFgAnx8AXwDAgEABwoBBm15X2FkZAAACgkBBwAgACABoAs=

wasm 和 wasm_instance 对象可以使用开发者控制台进行探索。

已在 Firefox 63.0b9 中检查。

Answer 2

This 是我在 Gist 上找到的一个注释很好的示例。将代码嵌入到您的 <script> 标记中，您将获得“单文件 WebAssembly html 演示”

为了方便，复制到这里：

// this code is from a simple add function in c:
//
// // hello.c
// int add(int a, int b) {
//    return a + b;
// }

//
// compiles it with emcc (http://webassembly.org/getting-started/developers-guide/)
// $ git clone https://github.com/juj/emsdk.git
// $ cd emsdk
// $ ./emsdk install latest
// $ ./emsdk activate latest
// $ source ./emsdk_env.sh --build=Release
//
// once installed:
//
// $ emcc hello.c -s ONLY_MY_CODE=1 -s WASM=1 -s EXPORTED_FUNCTIONS="['_add']" -o hello.js
//
// yes, not sure why we have to add '_' in front of the exported function.
// take the hello.wasm and serialize it to base64, e.g. using node

// const code = fs.readFileSync('./hello.wasm')
// code.toString('base64')
// AGFzbQEAAAABCwJgAX8AYAJ/fwF/An4HA2VudgZtZW1vcnkCAYACgAIDZW52BXRhYmxlAXABAAADZW52Cm1lbW9yeUJhc2UDfwADZW52CXRhYmxlQmFzZQN/AANlbnYIU1RBQ0tUT1ADfwADZW52CVNUQUNLX01BWAN/AANlbnYSYWJvcnRTdGFja092ZXJmbG93AAADAgEBBhMDfwEjAgt/ASMDC30BQwAAAAALBwgBBF9hZGQAAQkBAAo7ATkBB38jBCEIIwRBEGokBCMEIwVOBEBBEBAACyAAIQIgASEDIAIhBCADIQUgBCAFaiEGIAgkBCAGDws=


// https://www.npmjs.com/package/base64-arraybuffer
const chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

// Use a lookup table to find the index.
const lookup = new Uint8Array(256);
for (let i = 0; i < chars.length; i++) {
    lookup[chars.charCodeAt(i)] = i;
}

function decode(base64) {
  var bufferLength = base64.length * 0.75,
      len = base64.length, i, p = 0,
      encoded1, encoded2, encoded3, encoded4;

  if (base64[base64.length - 1] === "=") {
    bufferLength--;
    if (base64[base64.length - 2] === "=") {
      bufferLength--;
    }
  }

  var arraybuffer = new ArrayBuffer(bufferLength),
      bytes = new Uint8Array(arraybuffer);

  for (i = 0; i < len; i+=4) {
    encoded1 = lookup[base64.charCodeAt(i)];
    encoded2 = lookup[base64.charCodeAt(i+1)];
    encoded3 = lookup[base64.charCodeAt(i+2)];
    encoded4 = lookup[base64.charCodeAt(i+3)];

    bytes[p++] = (encoded1 << 2) | (encoded2 >> 4);
    bytes[p++] = ((encoded2 & 15) << 4) | (encoded3 >> 2);
    bytes[p++] = ((encoded3 & 3) << 6) | (encoded4 & 63);
  }

  return arraybuffer;
} 

// this is the serialized code.
const code = 'AGFzbQEAAAABCwJgAX8AYAJ/fwF/An4HA2VudgZtZW1vcnkCAYACgAIDZW52BXRhYmxlAXABAAADZW52Cm1lbW9yeUJhc2UDfwADZW52CXRhYmxlQmFzZQN/AANlbnYIU1RBQ0tUT1ADfwADZW52CVNUQUNLX01BWAN/AANlbnYSYWJvcnRTdGFja092ZXJmbG93AAADAgEBBhMDfwEjAgt/ASMDC30BQwAAAAALBwgBBF9hZGQAAQkBAAo7ATkBB38jBCEIIwRBEGokBCMEIwVOBEBBEBAACyAAIQIgASEDIAIhBCADIQUgBCAFaiEGIAgkBCAGDws='
const buffer = decode(code)

// bootstrap the env.
const memory = new WebAssembly.Memory({ initial: 256, maximum: 256 })
const importObj = {
    env: {
        abortStackOverflow: () => { throw new Error('overflow'); },
        table: new WebAssembly.Table({ initial: 0, maximum: 0, element: 'anyfunc' }),
        tableBase: 0,
        memory: memory,
        memoryBase: 1024,
        STACKTOP: 0,
        STACK_MAX: memory.buffer.byteLength,
    }
}

// instantiate
WebAssembly.instantiate(buffer, importObj)
  // take a look at that _add.
  .then(({module, instance}) => { console.log(instance.exports._add(1, 2)) })
  .catch((err) => { console.log(err.message) })