How to Execute a Callback after Asynchronous forEach Tasks Complete?

Executing a Callback after Asynchronous forEach Tasks are Complete

Problem

How can we execute a callback function once all asynchronous operations within a forEach loop have been completed?

Answer

Array.forEach does not provide an out-of-the-box solution for this scenario, but there are various approaches to achieve the desired functionality.

Using a Counter

<br>function callback() { console.log('all done'); }</p>
<p>var itemsProcessed = 0;</p>
<p>[1, 2, 3].forEach(item => {<br>  asyncFunction(item, () => {</p>
<div class="code" style="position:relative; padding:0px; margin:0px;"><pre class="brush:php;toolbar:false">itemsProcessed++;
if(itemsProcessed === array.length) {
  callback();
}

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});
});

This approach uses a counter that is incremented each time an asynchronous operation is completed. Once the counter reaches the total number of items in the array, the callback function is invoked.

Using ES6 Promises

• Synchronous Execution:
  

  <br>const requests = [1, 2, 3].reduce((promiseChain, item) => {<br>return promiseChain.then(() => new Promise((resolve) => {<br>  asyncFunction(item, resolve);<br>}));<br>}, Promise.resolve());</li></ul>
  <p>requests.then(() => console.log('done'))<br>

  In this example, we chain promises to guarantee that each asynchronous operation completes before the next one starts.

  • Asynchronous Execution:
    

    <br>const requests = [1,2,3].map((item) => {<br>return new Promise((resolve) => {<br>  asyncFunction(item, resolve);<br>});<br>})</li></ul>
    <p>Promise.all(requests).then(() => console.log('done'));<br>

    In this case, we use the Promise.all method to execute all asynchronous operations simultaneously and then invoke the callback when all of them are completed.

    Using an Async Library

    Asynchronous libraries like async provide mechanisms to express the desired functionality more elegantly.

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