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  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>Run a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI</title>





                const runAsync = fn => {
  const worker = new Worker(
    URL.createObjectURL(new Blob([`postMessage((${fn})());`]), {
      type: 'application/javascript; charset=utf-8'
  return new Promise((res, rej) => {
    worker.onmessage = ({ data }) => {
      res(data), worker.terminate();
    worker.onerror = err => {
      rej(err), worker.terminate();
const longRunningFunction = () => {
  let result = 0;
  for (let i = 0; i < 1000; i++) {
    for (let j = 0; j < 700; j++) {
      for (let k = 0; k < 300; k++) {
        result = result + i + j + k;
  return result;
runAsync(longRunningFunction).then(console.log); // 209685000000
runAsync(() => 10 ** 3).then(console.log); // 1000
let outsideVariable = 50;
runAsync(() => typeof outsideVariable).then(console.log); // 'undefined'