JavaScript: Run a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI

JavaScript: Exercise-151 with Solution

Write a JavaScript program to run a function in a separate thread using a Web Worker. This allows long running functions to not block the UI.

Note: 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 promise, listening for onmessage and onerror events and resolving the data posted back from the worker, or throwing an error.

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.

• 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.

Sample Solution:

JavaScript Code:

//#Source https://bit.ly/2neWfJ2

// Define the runAsync function
const runAsync = fn => {
  // Create a new worker with the given function
  const worker = new Worker(
    URL.createObjectURL(new Blob([`postMessage((${fn})());`]), {
      type: 'application/javascript; charset=utf-8'
    })
  );

  // Return a promise that resolves with the result of the function
  return new Promise((res, rej) => {
    // Listen for messages from the worker
    worker.onmessage = ({ data }) => {
      res(data), worker.terminate(); // Resolve the promise with the data and terminate the worker
    };
    // Listen for errors from the worker
    worker.onerror = err => {
      rej(err), worker.terminate(); // Reject the promise with the error and terminate the worker
    };
  });
};

// Define a long-running function
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;
};

// Example usage of runAsync with different functions
runAsync(longRunningFunction).then(console.log);  
runAsync(() => 10 ** 3).then(console.log);  
let outsideVariable = 50;
runAsync(() => typeof outsideVariable).then(console.log);

Sample Output:

1000
undefined

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-151-1 by w3resource (@w3resource) on CodePen.

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