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runAsync javascript Code Snippet in 2024

browserfunctionpromiseadvanced

Last Updated: 18 June 2024

Runs a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI.

  • Create a new Worker() using a Blob object URL, the contents of which should be the stringified version of the supplied function.
  • Immediately post the return value of calling the function back.
  • Return a new Promise(), listening for onmessage and onerror events and resolving the data posted back from the worker, or throwing an error.
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; }; /* NOTE: Since the function is running in a different context, closures are not supported. The function supplied to `runAsync` gets stringified, so everything becomes literal. All variables and functions must be defined inside. */ runAsync(longRunningFunction).then(console.log); // 209685000000 runAsync(() => 10 ** 3).then(console.log); // 1000 let outsideVariable = 50; runAsync(() => typeof outsideVariable).then(console.log); // 'undefined'

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