js-wasm-tools

js-wasm-tools compiles some of the API of wasm-tools to JavaScript and WebAssembly via wasm-bindgen. This offers low level tooling for WebAssembly in JavaScript, such as parsing WAT (WebAssembly Text Format) into bytes, translating the WebAssembly binary format to text, and more.

Install

npm install js-wasm-tools

Playground

You can try it out live on StackBlitz.com.

Usage

Using Vite:

import initWasmTools, * as wasmTools from 'js-wasm-tools';
import WASM_TOOLS_WASM_URL from 'js-wasm-tools/wasm_tools_js_bg.wasm?url';

await initWasmTools(WASM_TOOLS_WASM_URL);

const source = '(module)';

const binary = wasmTools.parseWat(source);

With Node.js:

import initWasmTools, * as wasmTools from 'js-wasm-tools';
import fs from 'node:fs';
import path from 'node:path';
import * as url from 'url';

const __dirname = url.fileURLToPath(new URL('.', import.meta.url));

const bytes = fs.readFileSync(path.join(__dirname, 'node_modules/js-wasm-tools/dist/js_wasm_tools_bg.wasm'));

await initWasmTools(bytes);

const source = '(module)';

const binary = wasmTools.parseWat(source);

console.log(binary);

API

parseWat(source: string): Uint8Array

Parses a string as the WebAssembly Text format, returning the WebAssembly binary format.

parseBytes(bytes: Uint8Array): Uint8Array

Parses bytes as either the WebAssembly Text format, or a binary WebAssembly module.

This function will attempt to interpret the given bytes as one of two options:

A utf-8 string which is a *.wat file to be parsed
A binary WebAssembly file starting with b"\0asm"

const encoder = new TextEncoder();

const bytes = wasmTools.parseWat(encoder.encode('(module)'));

expect(bytes).toEqual([0, 97, 115, 109, 1, 0, 0, 0]);

const bytes = wasmTools.parseWat([0, 97, 115, 109, 1, 0, 0, 0]);

expect(bytes).toEqual([0, 97, 115, 109, 1, 0, 0, 0]);

printBytes(bytes: Uint8Array): string

Prints a Wasm binary blob into a string which is its textual representation.

const wat = wasmTools.printBytes(new Uint8Array([0, 97, 115, 109, 1, 0, 0, 0]));

expect(wat).toEqual('(module)');

desugarWat(source: string): { wat: string, bytes: Uint8Array }

Parses a string as the WebAssembly Text format, and desugars the module, e.g. unfolding expressions.

const { wat, bytes } = wasmTools.desugarWat(`
  (module
    (func $foo
      (call $bar (i32.const 1) (i32.const 2))
    )
    (func $bar (param i32 i32))
  )
`);

expect(wat).toEqual(`
  (module
    (type (;0;) (func))
    (type (;1;) (func (param i32 i32)))
    (func $foo (;0;) (type 0)
      i32.const 1
      i32.const 2
      call $bar
    )
    (func $bar (;1;) (type 1) (param i32 i32))
  )
`);

validate(bytes: Uint8Array): Types

Test whether the given buffer contains a valid WebAssembly module or component, analogous to WebAssembly.validate in the JS API.

Upon success returns the type information for the top-level module or component.

const encoder = new TextEncoder();

const types = wasmTools.validate(
  encoder.encode(`
    (module
      (func $foo (result f32)
        f32.const 1
      )
      (func $bar (param i32 i32))
    )
  `)
);

expect(types).toEqual({
  types: [
    {
      params: [],
      results: ['f32'],
    },
    {
      params: ['i32', 'i32'],
      results: [],
    },
  ],
  functions: [
    {
      params: [],
      results: ['f32'],
    },
    {
      params: ['i32', 'i32'],
      results: [],
    },
  ],
  globals: [],
  memories: [],
  tables: [],
  elements: [],
});

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