How Can I Parallelize Asynchronous Calls in JavaScript using `async/await`?

Parallelizing Asynchronous Calls with await

When using the async/await syntax introduced in ES7, it's essential to understand that multiple await statements will execute sequentially rather than in parallel. This means that awaiting a result in one function call will suspend the execution until the previous call completes. To avoid this, there are several options.

One of the most straightforward methods in Node.js is to leverage the Promise.all() function. Promise.all() allows you to create a single promise that resolves when all the supplied promises resolve or rejects when any of them reject. By passing an array of promises to Promise.all(), you can ensure that all of them run concurrently.

Here's an example:

const someCall = () => new Promise((resolve) => setTimeout(() => resolve("some value"), 100));
const anotherCall = () => new Promise((resolve) => setTimeout(() => resolve("another value"), 200));

await Promise.all([someCall(), anotherCall()])
  .then((results) => {
    const [someResult, anotherResult] = results;
    // Do something with the results.
  });

In this example, both someCall() and anotherCall() will execute in parallel, and the results will be available in the results array.

An alternative approach is to use the async library, which provides additional features for asynchronous operations. The async.parallel() function allows you to specify an array of functions to run in parallel and a callback to be invoked once all functions have completed.

Here's an example using async.parallel():

const async = require("async");

const someCall = (callback) => setTimeout(() => callback(null, "some value"), 100);
const anotherCall = (callback) => setTimeout(() => callback(null, "another value"), 200);

async.parallel([someCall, anotherCall], (err, results) => {
  if (err) {
    // Handle any errors.
  } else {
    const [someResult, anotherResult] = results;
    // Do something with the results.
  }
});

Both Promise.all() and async.parallel() offer reliable methods for executing asynchronous functions in parallel. Choose the approach that best aligns with your project requirements and preferences.

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