How to Supply Metadata About Promises When Using Promise.all() in JavaScript

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Understanding the Problem

Let's start with the basic structure where you have an array of promises returned by a function, such as:

[[See Video to Reveal this Text or Code Snippet]]

The Need for Metadata

Imagine you need getArrayOfPromises() to return not just promises, but also some metadata about each promise. A simple initial approach might be to change its return value to include an array of objects, each containing a promise and its associated flag:

[[See Video to Reveal this Text or Code Snippet]]

The Solution: Mapping Promises with Metadata

Here's how to do it:

Map Each Promise: You can call the then() method on each promise, returning an object that includes the original value and the desired metadata.

Replace the Original Promises: After mapping, you replace the original array of promises with this new array that encapsulates both the promise value and the metadata.

Here’s the code for the solution:

[[See Video to Reveal this Text or Code Snippet]]

Example Code Walkthrough

Let's look at a complete example to illustrate this method:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Code:

sleep Function: Simulates an asynchronous operation which resolves after a set timeout.

getArrayOfPromises Function: Returns an array of promises generated by sleep.

Mapping: Each promise in the array is wrapped using map, which modifies the promise resolution to include both the resolved value and the metadata.

Conclusion

With this knowledge, you should be well-equipped to enhance your JavaScript promise handling strategies!