Compile WebAssembly .wat files to a common js module

  • wat2js

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Compile WebAssembly .wat files to a common js module
npm install -g wat2js

See https://github.com/WebAssembly/wabt 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

You can also pass arguments to wat2wasm:
wat2js example.wat -o example.js --watch -- --debug-names # add debug names section


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.