This is a simpe example on embedding wasm inside an offline single html page

hello-wasm.js

// 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) })