Use workers seamlessly

Workers are JavaScript’s version of threads. Workers are important to use as the main thread is already overloaded, especially on slower or older devices.

@surma/rollup-plugin-off-main-thread teaches Rollup about Workers. This plugin makes their use seamless using Comlink.

To avoid having to make new releases of this plugin with every release of Comlink or my OMT plugin, both of these modules have been declared as peer dependencies. This means you will have to explicitely add them to your dependency list:

$ npm install --save @surma/rollup-plugin-comlink @surma/rollup-plugin-off-main-thread comlink

// rollup.config.js
import comlink from "@surma/rollup-plugin-comlink";
import omt from "@surma/rollup-plugin-off-main-thread";
export default {
  input: ["src/main.js"],
  output: {
    dir: "dist",
    // You _must_ use either “amd” or “esm” as your format.
    // But note that only very few browsers have native support for
    // modules in workers.
    format: "amd",
  },
  plugins: [comlink(), omt()],
};

// worker.js
export function doMath(a, b) {
  return a + b;
}

Note: Importing individual exports currently does not work. comlink: modules only have one default export.

// main.js
import workerAPI from "comlink:./worker.js";
(async function () {
  const result = await workerAPI.doMath(40, 2);
  console.assert(result == 42);
})();

{
  // ...
  plugins: [comlink(options), omt()];
}

• marker: A string that is used as a prefix to mark a worker import. Default is comlink.
• useModuleWorkers: Use module workers (requires {format: "esm"}).

TypeScript can be taught to handle these pseudo-imports correctly and forward the types appropriately.

// main.ts
import workerAPI from "comlink:./worker.js";
console.log(await workerAPI.sayHello("surma"));
// This would fail to compile:
// console.log(await workerAPI.doesNotExit("surma"));

// worker.ts
export function sayHello(name: string): string {
  return `Hello ${name}!`;
}

// worker-modules.d.ts
declare module "comlink:./worker.js" {
  // Do *not* move this to a top-level import, as it will turn this
  // .d.ts file from an ambient module into a local module.
  const wrap: import("comlink").Remote<typeof import("./worker.js")>;
  export default wrap;
}

License Apache-2.0