index.js

const fs = require('fs')
const spawn = require('child_process').spawn
const through = require('through2')
const temp = require('tempy').file
const wrap = require('browserify-wrap')
function skip (a, b, next) { next() }

module.exports = wasmify

function wasmify (b, options) {
  options = Object.assign({}, options)

  // Add global wasm loader, used by the wasm imports
  b.plugin(wrap, {
    prefix: `\
      function _loadWasmModule (sync, src, imports) {
        var len = src.length
        var trailing = src[len-2] == '=' ? 2 : src[len-1] == '=' ? 1 : 0
        var buf = new Uint8Array((len * 3/4) - trailing)

        var _table = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
        var table = new Uint8Array(130)
        for (var c = 0; c < _table.length; c++) table[_table.charCodeAt(c)] = c

        for (var i = 0, b = 0; i < len; i+=4) {
          var second = table[src.charCodeAt(i+1)]
          var third = table[src.charCodeAt(i+2)]
          buf[b++] = (table[src.charCodeAt(i)] << 2) | (second >> 4)
          buf[b++] = ((second & 15) << 4) | (third >> 2)
          buf[b++] = ((third & 3) << 6) | (table[src.charCodeAt(i+3)] & 63)
        }

        if (sync) {
          var mod = new WebAssembly.Module(buf)
          return imports ? new WebAssembly.Instance(mod, imports) : mod
        }

        // return the the asynchronous WebAssembly.instantiate(buf) since this
        // is the primary API for compiling and instantiating WebAssembly code
        // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WebAssembly/instantiate
        return imports ? WebAssembly.instantiate(buf, imports) : WebAssembly.compile(buf)
      }
    `.trim()
  })

  // Transform wasm or source files
  b.transform(function (id, opts) {
    if (!opts) opts = {}
    const syncFiles = opts.sync ? opts.sync.map(path.resolve) : []
    if (!/\.wasm$/.test(id)) {
      return through()
    }

    return through(skip, function write () {
      fs.readFile(id, (err, code) => {
        if (err) return this.emit('error', err)
        const sync = syncFiles.indexOf(id) !== -1
        const wasm = code.toString('base64')
        // return a function that take into account the imports
        // an example of an `imports` object:
        // const memory = new WebAssembly.Memory({ initial: 512 })
        // const imports = {
        //  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,
        //   }
        // }

        this.push(`module.exports=function(imports){return _loadWasmModule(${sync}, '${wasm}', imports)}`)
        this.push(null)
      })
    })
  })

  return b
}