Runable at https://githubproxy.samuelcolvin.workers.dev/samuelcolvin/0a3c6545c50ae0ca2440f891d0631035/raw/1ecc2c78ca4003db23de6dcf9044187f60778999/webworker_demo.html

webworker_demo.html

<h1>Web worker demo</h1>

<h3>Write Code:</h3>
<textarea id="code" rows="10" cols="80">return "hello world";</textarea>
<button id="run">Run</button>

<h3>Output:</h3>
<pre id="output"></pre>


<script>
  const code = document.getElementById('code');
  const run = document.getElementById('run');
  const output = document.getElementById('output');
  const worker = new Worker('worker.js');

  run.addEventListener('click', function() {
    output.textContent = '';
    worker.postMessage(code.value);
  });

  worker.addEventListener('message', function(e) {
    console.log(e.data);
    if (e.data.result) {
      output.textContent += `Result: ${e.data.result}\n`
    } else {
      output.textContent += `Error: ${e.data.error}\n`;
    }
  });
</script>

worker.js

onmessage = function(e) {
  console.log('Message received from main script', e);
  const code = e.data;
  console.log('running code:', {code});
  eval(`(async () => { ${code} })()`).then((result) => {
    console.log('code result:', result);
    postMessage({result: JSON.stringify(result)});
  }).catch((error) => {
    console.error('code error:', error);
    postMessage({error: JSON.stringify(error.toString())});
  })
}