Compile WebAssembly .wat files to a common js module
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.gitignore first commit Jun 26, 2017
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example.js Using extracted wasm2js code (#3) Nov 18, 2017
example.wat first commit Jun 26, 2017
index.js Using extracted wasm2js code (#3) Nov 18, 2017
package.json 2.0.0 Jun 9, 2018


Compile WebAssembly .wat files to a common js module

npm install -g wat2js

See for more WebAssembly goodies.

Currently requires the wat2wasm program to be installed globally. If you don't have that already you can get that by installing the webassembly binary toolkit by using this little helper


First make a basic WebAssembly .wat file

;; example.wat
  ;; var result = add(a, b)
  (func (export "add") (param $a i32) (param $b i32) (result i32)
    ;; return a + b
      (get_local $a)
      (get_local $b)

Then compile it to WebAssembly and wrap in a common js loader by doing

wat2js example.wat -o example.js

To run the WebAssembly simply do:

var example = require('./example.js')() // load the wasm
if (!example) throw new Error('WebAssembly not supported by your runtime')

var result = example.exports.add(1, 2)
console.log('1 + 2 = ' + result)

To keep recompiling the .wat file when it changes pass the --watch option as well

wat2js example.wat -o example.js --watch # recompile when example.wat changes


var mod = require('./compiled-wat.js')([options])

Loads your WebAssembly module. If WebAssembly is not supported by the runtime, null is returned.

Options include:

  imports: {...} // import objected forwared to WASM,
  async: true // force async loading.

Note that if your WASM is larger than 4kb, some browsers might force async loading.

mod looks like this

  exports: {...}, // exports WASM functions
  memory: Uint8Array, // exports.memory wrapped in a uint8array (if exported)
  buffer: Uint8Array, // the WASM module as a buffer
  onload: onload(cb), // function you can call to wait for async loading
  realloc: realloc(bytes) // reallocate the memory buffer to a new size

In case of async loading exports and memory will be null until the module has been loaded.