Callback after all asynchronous forEach callbacks are completed

javascript

async-programming

control-flow

promises

byAnton Shumikhin·Jan 31, 2025

Execute your callback after your sequence of asynchronous tasks by adopting the Promise approach and aggregating them. Promise.all could then help ensure that your final callback only runs after all promises get resolved.

Here is a simple example:

const asyncTasks = [/* "Async tasks? More like 'a sync task', right?" */];
const promises = asyncTasks.map(task => new Promise((resolve) => task().then(result => { 
  console.log("Task completed. I'm resolving, therefore I exist. 🤔");
  resolve(result);
})));

Promise.all(promises).then(() => {
  console.log('Looks like all tasks are done.;');
  // Place your logic for final callback here
});

Focus:

Ensure Promise.all that all promises have been covered
Ensure every async task has been mapped to a promise
Only execute callback after Promise.all is resolved

Sync & Async: the duality of tasks

Working with asynchronous operations nested within synchronous loops like Array.forEach could be confusing. The solution lies in control flow devices like Promise.all. Beware of the ancient tribal scriptures, they speak of race conditions when dealing with async operations and counters, Promises are immune to this elusive evil.

Async task execution order: the unruly child

Promises can be a tough cookie. The completion order is not guaranteed, quite similar to sibling rivalries. If sequential execution is important, make sure the state for each async function's completion callback can stand independently.

Async/Await: the saviors

The holy grail of asynchronous logic lies in the serenity brought by async/await. With this, your code becomes more readable, and handling life’s unpleasant surprises, aka exceptions, becomes a breeze with try/catch blocks.

Async library: the best friend you didn't know you had

When the going gets tough, the async library gets going. It comes with handy tools like async.each, async.parallel, and async.series which take on the burdens of boilerplate logic, leaving room for strategizing your business logic.

ES2018's for await...of: the unsung hero

With ES2018 came yet another helper in handling async code, the for await...of loop. It allows smooth iteration over async iterable objects simplifying control flow significantly.

Async Iterators: The new kids on the block

Want to control the async execution flow? Say hello to async iterators. When combined with for await...of it will listen to your commands about when an async operation should stop and continue.

Item done callbacks: the individual cheerleaders

Sometimes, each async task needs its own cheerleader – the itemDone callback. If that’s on your wishlist, design every async function to enact the itemDone callback on task completion keeping in mind the freedom of the callback to enforce rules in any order.

No-utility async forEach handling: the diy task

When Promise.all or async libraries are unavailable, revert to "good ol' basics". Manage async forEach execution with a counter, but keep your wits about you while handling errors and updating counters.

Analyzing the enemy: async/await pitfalls

Async/await is not a universal solution. If it’s unsupported in an environment or incompatible with a library, you’ve to use an alternative tool. Recognizing the right tool is sometimes the most challenging task of all.

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