How to Execute a Callback After All Asynchronous Callbacks Within a 'forEach' Loop Finish?

Asynchronous Callback Execution after 'forEach' Iteration

Query:

How can a callback be executed after all asynchronous callbacks of a 'forEach' loop are completed?

Solution:

Array.forEach does not inherently support this functionality. However, there are several alternative approaches to achieve this goal:

1. Counter:

Keep track of the number of processed items using a counter. Increment the counter in the callback of each asynchronous operation and invoke the final callback when the counter reaches the total number of items.

2. Promises (ES6):

a. Sequential Execution:

Chain promises in sequence to guarantee synchronous execution of asynchronous tasks, ensuring each item is processed in the order they appear in the array.

b. Parallel Execution:

Use the Promise.all() method to execute all asynchronous tasks in parallel without guaranteeing execution order.

3. Async Library:

Popular libraries like Async.js provide mechanisms to express the required behavior, such as Async#series() and Async#parallel().

Original Example Implementation (Synchronous):

The original code in the question exemplified a synchronous scenario, and the following implementation can be used:

posts.foreach(function(v, i) {
  res.write(v + ". index " + i);
});

res.end();

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