a trick to embed javascript resource in html

inline-worker.html

  <script id="worker" src="data:,">
    // the empty "src" prevents code inside this block from being executed!
    // this is the source code of the worker.

    postMessage("Hello world!")

  </script>

  <script>
    var blob = new Blob([document.getElementById('worker').textContent],
                        {type: 'application/javascript'})

    var worker = new Worker(URL.createObjectURL(blob), {type: 'module'})

    worker.onmessage = (ev) => {
      console.log(ev.data)
    }
  </script>

Note

{type: 'module'} is only allowed in secure context (localhost / https).
However without this option, this code can run in file://.