[RFC] Add npm library mode

[mizchi]

This PR is proposal to add npm library mode build.

API Proposal

It generates them.

• worker-dom/dist/lib/main.mjs: export attachWorker(element: HTMLElement, worker: Worker): void
• worker-dom/dist/lib/worker.mjs: export ready: Promise<void> (DOM is ready to touch)

Background

I think worker-dom can be general purpose library for frontend performance, but today's api does not fit webpack. Under using webpack, there are many ways to bundle worker code like worker-plugin and worker-loader.

This proposal provides seamless way with webpack.

Example

with worker-plugin (https://github.com/GoogleChromeLabs/worker-plugin)

// index.js
import { attachWorker } from '@ampproject/worker-dom/dist/lib/main.mjs';

const el = document.createElement('main');
el.innerHTML = `
<div>
  <h1>main</h1>
  <button>click</button>
</div>
`;
document.body.appendChild(el);

// bundle worker code with worker-plugin
const worker = new Worker('./worker.js', { type: 'module' });

attachWorker(el, worker);

// worker.js
import { ready } from '@ampproject/worker-dom/dist/lib/worker.mjs';

async function run() {
  await ready;

  // dom mutation
  const el = document.createElement('h2');
  el.textContent = 'hello from worker';
  document.body.appendChild(el);

  // handler
  const button = document.querySelector('button');
  button.onclick = (ev) => {
    console.log('button:onclick', ev);
  };
}

run();

See full code demo/as-webpack-lib

Working Demo

https://worker-dom-as-lib-example.netlify.app/

sample repository (use published @mizchi/worker-dom)

https://github.com/mizchi/worker-dom-webpack-example

https://wizardly-benz-02c23e.netlify.app/

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[googlebot]

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[mizchi]

WIP: I copied it from WorkerContext and patched. Is there clear way?

[mizchi]

Maybe adding TransferrableKeys and some types like Initializer are better but at first makes it simple

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