as-loader

as-loader

AssemblyScript loader for webpack

⚠️ In development ⚠️

Installation

This loader requires minimum AssemblyScript 0.18, Node.js 12 and webpack 4 or webpack 5

# with npm
npm install --save-dev as-loader

# with yarn
yarn add --dev as-loader

If you don't have AssemblyScript installed yet:

# with npm
npm install --save-dev assemblyscript

# with yarn
yarn add --dev assemblyscript

The minimal webpack.config.js:

module.exports = {
  entry: "src/index.ts",
  resolve: {
    extensions: [".ts", ".js"],
  },
  module: {
    rules: [
      {
        test: /\.ts$/,
        include: path.resolve(__dirname, "src/assembly"),
        loader: "as-loader",
        options: {
          // optional loader and compiler options
        }
      },
      {
        test: /\.ts$/,
        exclude: path.resolve(__dirname, "src/assembly"),
        loader: "ts-loader",
      },
    ],
  },
};

Usage

By default, the loader emits .wasm file (+ .wasm.map if source maps are enabled) and creates CommonJS module that exports URL to the emitted .wasm file.

If you enable fallback option, the loader will emit additional .js file (+ .js.map if source maps are enabled) and will expose async fallback() function which dynamically imports fallback module.

To simplify loading logic, you can use as-loader/runtime loader which uses @assemblyscript/loader under the hood. The loader provides correct types, checks for WebAssembly support, and uses fallback if available.

import * as myModule from "./assembly/myModule";
import { instantiate } from "as-loader/runtime/web";

async function loadAndRun() {
  const { exports } = await instantiate(myModule);

  exports.myFunction(100);
}

loadAndRun();

Alternatively, you can use exported URL directly:

import * as myModule from "./assembly/myModule";
import { instantiate } from "@assemblyscript/loader";

async function loadAndRun() {
  const { exports } = await instantiate<typeof myModule>(
    // workaround for TypeScript
    fetch((myModule as unknown) as string)
  );

  exports.myFunction(100);
}

loadAndRun();

Binding

There are 2 aspects that you have to consider when interacting with WebAssembly module:

1. WebAssembly doesn't support function arguments and returns others than number and boolean yet. Because of that, you have to manually translate between WebAssembly pointers and JavaScript objects. The alternative solution is to use as-bind library which does this automatically for string and array types (doesn't support objects yet).
2. WebAssembly doesn't provide GC yet (proposal) - to manage memory, AssemblyScript offers very lightweight GC implementation. If you use it (see runtime option - it's "incremental" by default), you have to manually __pin and __unpin pointers to instruct GC if given data can be collected or not.

The as-loader/runtime uses @assemblyscript/loader under the hood - see the docs for more information.

Binding code example:

// ./src/assembly/sayHello.ts
export function sayHello(firstName: string, lastName: string): string {
  return `Hello ${firstName} ${lastName}!`;
}

// ./src/sayHello.ts
import * as sayHelloModule from "./assembly/sayHello";
import { instantiate } from "as-loader/runtime";

export async function loadModule(): Promise<typeof sayHelloModule> {
  // this example doesn't use fallback so TypeScript knows that it's only WASM module
  const { exports } = await instantiate(sayHelloModule, fetch, undefined, false);
  const { __pin, __unpin, __newString, __getString } = exports;

  function sayHello(firstName: string, lastName: string): string {
    const firstNamePtr = __pin(__newString(firstName));
    const lastNamePtr = __pin(__newString(lastName));
    const result = __getString(
      exports.sayHello(firstNamePtr, lastNamePtr)
    );

    __unpin(firstNamePtr);
    __unpin(lastNamePtr);

    return result;
  }

  return { sayHello };
}

Options

Loader Options

Name	Type	Description
name	string	Output asset name template, [name].[contenthash].wasm by default.
raw	boolean	If true, returns binary instead of emitting file. Use for chaining with other loaders.
fallback	boolean	If true, creates additional JavaScript file which can be used if WebAssembly is not supported.

Compiler Options

Options passed to the AssemblyScript compiler.

Name	Type	Description
debug	boolean	Enables debug information in emitted binaries.
optimizeLevel	number	How much to focus on optimizing code. [0-3]
shrinkLevel	number	How much to focus on shrinking code size. [0-2]
coverage	boolean	Re-optimizes until no further improvements can be made.
noAssert	boolean	Replaces assertions with just their value without trapping.
importMemory	boolean	Imports the memory provided as 'env.memory'.
noExportMemory	boolean	Does not export the memory as 'memory'.
initialMemory	number	Sets the initial memory size in pages.
maximumMemory	number	Sets the maximum memory size in pages.
sharedMemory	boolean	Declare memory as shared. Requires maximumMemory.
importTable	boolean	Imports the function table provided as 'env.table'.
exportTable	boolean	Exports the function table as 'table'.
runtime	string	Specifies the runtime variant to include in the program. Available runtimes are: "incremental" (default), "minimal", "stub"
exportRuntime	boolean	Exports the runtime helpers (__new, __collect etc.). Enabled by default.
explicitStart	boolean	Exports an explicit '_start' function to call.
enable	string[]	Enables WebAssembly features being disabled by default. Available features are: "sign-extension", "bulk-memory", "simd", "threads", "reference-types", "gc"
disable	string[]	Disables WebAssembly features being enabled by default. Available features are: "mutable-globals"
lowMemoryLimit	boolean	Enforces very low (<64k) memory constraints.
memoryBase	number	Sets the start offset of emitted memory segments.
tableBase	number	Sets the start offset of emitted table elements.
trapMode	string	Sets the trap mode to use. Available modes are: "allow", "clamp", "js"
noValidate	boolean	Skips validating the module using Binaryen.

License

MIT